Apparatus, a method and a computer program for omnidirectional video

ABSTRACT

There are disclosed various methods, apparatuses and computer program products for video encoding and decoding. In some embodiments an encoding method comprises obtaining information of a region (63) for overlaying at least a part of an omnidirectional video (61), information of a current viewport (62) in the omnidirectional video (61), and information of an overlaying method to determine whether to overlay a part of the current viewport (62) or the whole current viewport (62) by the overlaying region (63). The method may further comprise encoding information of the overlaying region (63), the current viewport (62) and the overlaying method. In some embodiments a decoding method comprises receiving and decoding information of a region (63) for overlaying at least a part of an omnidirectional video (61), information of a current viewport (62) in the omnidirectional video (61), and information of an overlaying method to determine whether to overlay a part of the current viewport (62) or the whole current viewport (62) by the overlaying region (63). The method may further comprise examining the decoded information of the overlaying method. If the examining reveals that the overlaying method is a partial overlaying method, overlaying a part of the image information of the current viewport (62) by the image information of the overlaying region (63), or if the examining reveals that the overlaying method is a whole overlaying method, overlaying the whole current viewport (62) by the image information of the overlaying region (63).

RELATED APPLICATION

This application claims priority to PCT Application No.PCT/FI2019/050027, filed on Jan. 14, 2019, which claims priority toFinland Application No. 20185044, filed on Jan. 17, 2018, each of whichis incorporated herein by reference in its entirety.

TECHNICAL FIELD

The present invention relates to an apparatus, a method and a computerprogram for omnidirectional video/image coding, decoding, file writing,file reading, and delivery.

BACKGROUND

This section is intended to provide a background or context to theinvention that is recited in the claims. The description herein mayinclude concepts that could be pursued, but are not necessarily onesthat have been previously conceived or pursued. Therefore, unlessotherwise indicated herein, what is described in this section is notprior art to the description and claims in this application and is notadmitted to be prior art by inclusion in this section.

A video coding system may comprise an encoder that transforms an inputvideo into a compressed representation suited for storage/transmissionand a decoder that can uncompress the compressed video representationback into a viewable form. The encoder may discard some information inthe original video sequence in order to represent the video in a morecompact form, for example, to enable the storage/transmission of thevideo information at a lower bitrate than otherwise might be needed.

Various technologies for providing three-dimensional (3D) video contentare currently investigated and developed. Especially, intense studieshave been focused on various multiview applications wherein a viewer isable to see only one pair of stereo video from a specific viewpoint andanother pair of stereo video from a different viewpoint. One of the mostfeasible approaches for such multiview applications has turned out to besuch wherein only a limited number of input views, e.g. a mono or astereo video plus some supplementary data, is provided to a decoder sideand all required views are then rendered (i.e. synthesized) locally bythe decoder to be displayed on a display.

In the encoding of 3D video content, video compression systems, such asAdvanced Video Coding standard (H.264/AVC), the Multiview Video Coding(MVC) extension of H.264/AVC or scalable extensions of HEVC (HighEfficiency Video Coding) can be used.

SUMMARY

Some embodiments provide a method for encoding and decoding videoinformation. In some embodiments of the present invention there isprovided a method, apparatus and computer program product for videocoding as well as decoding.

Various aspects of examples of the invention are provided in thedetailed description.

According to a first aspect, there is provided a method comprising:

obtaining information of a region for overlaying at least a part of anomnidirectional video;

obtaining information of a current viewport in the omnidirectionalvideo;

obtaining information of an overlaying method to determine whether tooverlay a part of the current viewport or the whole current viewport bythe overlaying region;

encoding information of the overlaying region, the current viewport andthe overlaying method.

An apparatus according to a second aspect comprises at least oneprocessor and at least one memory, said at least one memory stored withcode thereon, which when executed by said at least one processor, causesthe apparatus to perform at least:

obtain information of a region for overlaying at least a part of anomnidirectional video;

obtain information of a current viewport in the omnidirectional video;

obtain information of an overlaying method to determine whether tooverlay a part of the current viewport or the whole current viewport bythe overlaying region;

encode information of the overlaying region, the current viewport andthe overlaying method.

A computer readable storage medium according to a third aspect comprisescode for use by an apparatus, which when executed by a processor, causesthe apparatus to perform:

obtain information of a region for overlaying at least a part of anomnidirectional video;

obtain information of a current viewport in the omnidirectional video;

obtain information of an overlaying method to determine whether tooverlay a part of the current viewport or the whole current viewport bythe overlaying region;

encode information of the overlaying region, the current viewport andthe overlaying method.

An apparatus according to a fourth aspect comprises:

means for obtaining information of a region for overlaying at least apart of an omnidirectional video;

means for obtaining information of a current viewport in theomnidirectional video;

means for obtaining information of an overlaying method to determinewhether to overlay a part of the current viewport or the whole currentviewport by the overlaying region;

means for encoding information of the overlaying region, the currentviewport and the overlaying method.

A method according to a fifth aspect comprises:

receiving information of a region for overlaying at least a part of anomnidirectional video;

receiving information of a current viewport in the omnidirectionalvideo;

receiving information of an overlaying method to determine whether tooverlay a part of the current viewport or the whole current viewport bythe overlaying region;

decoding the information of the overlaying method;

decoding image information of the current viewport;

decoding image information of the overlaying region;

examining the decoded information of the overlaying method;

if the examining reveals that the overlaying method is a partialoverlaying method, overlaying a part of the image information of thecurrent viewport by the image information of the overlaying region; or

if the examining reveals that the overlaying method is a wholeoverlaying method, overlaying the whole current viewport by the imageinformation of the overlaying region.

An apparatus according to a sixth aspect comprises at least oneprocessor and at least one memory, said at least one memory stored withcode thereon, which when executed by said at least one processor, causesthe apparatus to perform at least:

receive information of a region for overlaying at least a part of anomnidirectional video;

receive information of a current viewport in the omnidirectional video;

receive information of an overlaying method to determine whether tooverlay a part of the current viewport or the whole current viewport bythe overlaying region;

decode the information of the overlaying method;

decode image information of the current viewport;

decode image information of the overlaying region;

examine the decoded information of the overlaying method;

overlay a part of the image information of the current viewport by theimage information of the overlaying region if the examining reveals thatthe overlaying method is a partial overlaying method; or

overlay the whole current viewport by the image information of theoverlaying region if the examining reveals that the overlaying method isa whole overlaying method.

A computer readable storage medium according to a seventh aspectcomprises code for use by an apparatus, which when executed by aprocessor, causes the apparatus to perform:

receive information of a region for overlaying at least a part of anomnidirectional video;

receive information of a current viewport in the omnidirectional video;

receive information of an overlaying method to determine whether tooverlay a part of the current viewport or the whole current viewport bythe overlaying region;

decode the information of the overlaying method;

decode image information of the current viewport;

decode image information of the overlaying region;

examine the decoded information of the overlaying method;

overlay a part of the image information of the current viewport by theimage information of the overlaying region if the examining reveals thatthe overlaying method is a partial overlaying method; or

overlay the whole current viewport by the image information of theoverlaying region if the examining reveals that the overlaying method isa whole overlaying method.

An apparatus according to an eight aspect comprises:

means for

receiving information of a region for overlaying at least a part of anomnidirectional video;

means for receiving information of a current viewport in theomnidirectional video;

means for receiving information of an overlaying method to determinewhether to overlay a part of the current viewport or the whole currentviewport by the overlaying region;

means for decoding the information of the overlaying method;

means for decoding image information of the current viewport;

means for decoding image information of the overlaying region;

means for examining the decoded information of the overlaying method;

means for overlaying a part of the image information of the currentviewport by the image information of the overlaying region, if theexamining reveals that the overlaying method is a partial overlayingmethod; and

means for overlaying the whole current viewport by the image informationof the overlaying region, if the examining reveals that the overlayingmethod is a whole overlaying method.

Further aspects include at least apparatuses and computer programproducts/code stored on a non-transitory memory medium arranged to carryout the above methods.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of example embodiments of the presentinvention, reference is now made to the following descriptions taken inconnection with the accompanying drawings in which:

FIG. 1 a shows an example of a multi-camera system as a simplified blockdiagram, in accordance with an embodiment;

FIG. 1 b shows a perspective view of a multi-camera system, inaccordance with an embodiment;

FIG. 2 a illustrates image stitching, projection, and mapping processes,in accordance with an embodiment;

FIG. 2 b illustrates a process of forming a monoscopic equirectangularpanorama picture, in accordance with an embodiment;

FIG. 3 shows an example of mapping a higher resolution sampled frontface of a cube map on the same packed virtual reality frame as othercube faces, in accordance with an embodiment;

FIG. 4 shows an example of merging coded rectangle sequences into abitstream, in accordance with an embodiment;

FIG. 5 shows an example how extractor tracks can be used for tile-basedomnidirectional video streaming, in accordance with an embodiment;

FIG. 6 a illustrates an example of an omnidirectional video/image froman event, in accordance with an embodiment;

FIG. 6 b illustrates a user's viewport of FIG. 6 a , in accordance withan embodiment;

FIG. 6 c illustrates another example of overlaying a whole 360-degreevideo on a user's current viewport, in accordance with an embodiment;

FIG. 6 d illustrates an example of an overlay text, in accordance withan embodiment;

FIG. 7 a shows an example of a hierarchical data model used in DASH;

FIG. 7 b shows an example of an omnidirectional streaming system;

FIG. 8 a shows a schematic diagram of an encoder suitable forimplementing embodiments of the invention;

FIG. 8 b shows a schematic diagram of a decoder suitable forimplementing embodiments of the invention;

FIG. 9 a shows some elements of a video encoding section, in accordancewith an embodiment;

FIG. 9 b shows a video decoding section, in accordance with anembodiment;

FIG. 10 a shows a flow chart of an encoding method, in accordance withan embodiment;

FIG. 10 b shows a flow chart of a decoding method, in accordance with anembodiment;

FIG. 11 shows a schematic diagram of an example multimedia communicationsystem within which various embodiments may be implemented;

FIG. 12 shows schematically an electronic device employing embodimentsof the invention;

FIG. 13 shows schematically a user equipment suitable for employingembodiments of the invention;

FIG. 14 further shows schematically electronic devices employingembodiments of the invention connected using wireless and wired networkconnections.

DETAILED DESCRIPTION OF SOME EXAMPLE EMBODIMENTS

In the following, several embodiments of the invention will be describedin the context of one video coding arrangement. It is to be noted,however, that the invention is not limited to this particulararrangement. In fact, the different embodiments have applications widelyin any environment where improvement of coding when switching betweencoded fields and frames is desired. For example, the invention may beapplicable to video coding systems like streaming systems, DVD players,digital television receivers, personal video recorders, systems andcomputer programs on personal computers, handheld computers andcommunication devices, as well as network elements such as transcodersand cloud computing arrangements where video data is handled.

In the following, several embodiments are described using the conventionof referring to (de)coding, which indicates that the embodiments mayapply to decoding and/or encoding.

The Advanced Video Coding standard (which may be abbreviated AVC orH.264/AVC) was developed by the Joint Video Team (JVT) of the VideoCoding Experts Group (VCEG) of the Telecommunications StandardizationSector of International Telecommunication Union (ITU-T) and the MovingPicture Experts Group (MPEG) of International Organisation forStandardization (ISO)/International Electrotechnical Commission (IEC).The H.264/AVC standard is published by both parent standardizationorganizations, and it is referred to as ITU-T Recommendation H.264 andISO/IEC International Standard 14496-10, also known as MPEG-4 Part 10Advanced Video Coding (AVC). There have been multiple versions of theH.264/AVC standard, each integrating new extensions or features to thespecification. These extensions include Scalable Video Coding (SVC) andMultiview Video Coding (MVC).

The High Efficiency Video Coding standard (which may be abbreviated HEVCor H.265/HEVC) was developed by the Joint Collaborative Team—VideoCoding (JCT-VC) of VCEG and MPEG. The standard is published by bothparent standardization organizations, and it is referred to as ITU-TRecommendation H.265 and ISO/IEC International Standard 23008-2, alsoknown as MPEG-H Part 2 High Efficiency Video Coding (HEVC). Extensionsto H.265/HEVC include scalable, multiview, three-dimensional, andfidelity range extensions, which may be referred to as SHVC, MV-HEVC,3D-HEVC, and REXT, respectively. The references in this description toH.265/HEVC, SHVC, MV-HEVC, 3D-HEVC and REXT that have been made for thepurpose of understanding definitions, structures or concepts of thesestandard specifications are to be understood to be references to thelatest versions of these standards that were available before the dateof this application, unless otherwise indicated.

Some key definitions, bitstream and coding structures, and concepts ofH.264/AVC and HEVC and some of their extensions are described in thissection as an example of a video encoder, decoder, encoding method,decoding method, and a bitstream structure, wherein the embodiments maybe implemented. Some of the key definitions, bitstream and codingstructures, and concepts of H.264/AVC are the same as in HEVCstandard—hence, they are described below jointly. The aspects of theinvention are not limited to H.264/AVC or HEVC or their extensions, butrather the description is given for one possible basis on top of whichthe invention may be partly or fully realized.

In the description of existing standards as well as in the descriptionof example embodiments, a syntax element may be defined as an element ofdata represented in the bitstream. A syntax structure may be defined aszero or more syntax elements present together in the bitstream in aspecified order.

Similarly to many earlier video coding standards, the bitstream syntaxand semantics as well as the decoding process for error-free bitstreamsare specified in H.264/AVC and HEVC. The encoding process is notspecified, but encoders must generate conforming bitstreams. Bitstreamand decoder conformance can be verified with the Hypothetical ReferenceDecoder (HRD). The standards contain coding tools that help in copingwith transmission errors and losses, but the use of the tools inencoding is optional and no decoding process has been specified forerroneous bitstreams.

The elementary unit for the input to an H.264/AVC or HEVC encoder andthe output of an H.264/AVC or HEVC decoder, respectively, is a picture.A picture given as an input to an encoder may also be referred to as asource picture, and a picture decoded by a decoder may be referred to asa decoded picture.

The source and decoded pictures may each be comprised of one or moresample arrays, such as one of the following sets of sample arrays:

-   -   Luma (Y) only (monochrome).    -   Luma and two chroma (YCbCr or YCgCo).    -   Green, Blue and Red (GBR, also known as RGB).    -   Arrays representing other unspecified monochrome or tri-stimulus        color samplings (for example, YZX, also known as XYZ).

In the following, these arrays may be referred to as luma (or L or Y)and chroma, where the two chroma arrays may be referred to as Cb and Cr;regardless of the actual color representation method in use. The actualcolor representation method in use may be indicated e.g. in a codedbitstream e.g. using the Video Usability Information (VUI) syntax ofH.264/AVC and/or HEVC. A component may be defined as an array or asingle sample from one of the three sample arrays (luma and two chroma)or the array or a single sample of the array that compose a picture inmonochrome format.

In H.264/AVC and HEVC, a picture may either be a frame or a field. Aframe comprises a matrix of luma samples and possibly the correspondingchroma samples. A field is a set of alternate sample rows of a frame.Fields may be used as encoder input for example when the source signalis interlaced. Chroma sample arrays may be absent (and hence monochromesampling may be in use) or may be subsampled when compared to lumasample arrays. Some chroma formats may be summarized as follows:

-   -   In monochrome sampling there is only one sample array, which may        be nominally considered the luma array.    -   In 4:2:0 sampling, each of the two chroma arrays has half the        height and half the width of the luma array.    -   In 4:2:2 sampling, each of the two chroma arrays has the same        height and half the width of the luma array.    -   In 4:4:4 sampling when no separate color planes are in use, each        of the two chroma arrays has the same height and width as the        luma array.

In H.264/AVC and HEVC, it is possible to code sample arrays as separatecolor planes into the bitstream and respectively decode separately codedcolor planes from the bitstream. When separate color planes are in use,each one of them is separately processed (by the encoder and/or thedecoder) as a picture with monochrome sampling.

When chroma subsampling is in use (e.g. 4:2:0 or 4:2:2 chroma sampling),the location of chroma samples with respect to luma samples may bedetermined in the encoder side (e.g. as pre-processing step or as partof encoding). The chroma sample positions with respect to luma samplepositions may be pre-defined for example in a coding standard, such asH.264/AVC or HEVC, or may be indicated in the bitstream for example aspart of VUI of H.264/AVC or HEVC.

Generally, the source video sequence(s) provided as input for encodingmay either represent interlaced source content or progressive sourcecontent. Fields of opposite parity have been captured at different timesfor interlaced source content. Progressive source content containscaptured frames. An encoder may encode fields of interlaced sourcecontent in two ways: a pair of interlaced fields may be coded into acoded frame or a field may be coded as a coded field. Likewise, anencoder may encode frames of progressive source content in two ways: aframe of progressive source content may be coded into a coded frame or apair of coded fields. A field pair or a complementary field pair may bedefined as two fields next to each other in decoding and/or outputorder, having opposite parity (i.e. one being a top field and anotherbeing a bottom field) and neither belonging to any other complementaryfield pair. Some video coding standards or schemes allow mixing of codedframes and coded fields in the same coded video sequence. Moreover,predicting a coded field from a field in a coded frame and/or predictinga coded frame for a complementary field pair (coded as fields) may beenabled in encoding and/or decoding.

A partitioning may be defined as a division of a set into subsets suchthat each element of the set is in exactly one of the subsets. A picturepartitioning may be defined as a division of a picture into smallernon-overlapping units. A block partitioning may be defined as a divisionof a block into smaller non-overlapping units, such as sub-blocks. Insome cases term block partitioning may be considered to cover multiplelevels of partitioning, for example partitioning of a picture intoslices, and partitioning of each slice into smaller units, such asmacroblocks of H.264/AVC. It is noted that the same unit, such as apicture, may have more than one partitioning. For example, a coding unitof HEVC may be partitioned into prediction units and separately byanother quadtree into transform units.

A coded picture is a coded representation of a picture.

Video coding standards and specifications may allow encoders to divide acoded picture to coded slices or alike. In-picture prediction istypically disabled across slice boundaries. Thus, slices can be regardedas a way to split a coded picture to independently decodable pieces. InH.264/AVC and HEVC, in-picture prediction may be disabled across sliceboundaries. Thus, slices can be regarded as a way to split a codedpicture into independently decodable pieces, and slices are thereforeoften regarded as elementary units for transmission. In many cases,encoders may indicate in the bitstream which types of in-pictureprediction are turned off across slice boundaries, and the decoderoperation takes this information into account for example whenconcluding which prediction sources are available. For example, samplesfrom a neighbouring macroblock or CU may be regarded as unavailable forintra prediction, if the neighbouring macroblock or CU resides in adifferent slice.

In H.264/AVC, a macroblock is a 16×16 block of luma samples and thecorresponding blocks of chroma samples. For example, in the 4:2:0sampling pattern, a macroblock contains one 8×8 block of chroma samplesper each chroma component. In H.264/AVC, a picture is partitioned to oneor more slice groups, and a slice group contains one or more slices. InH.264/AVC, a slice consists of an integer number of macroblocks orderedconsecutively in the raster scan within a particular slice group.

When describing the operation of HEVC, the following terms may be used.A coding block may be defined as an N×N block of samples for some valueof N such that the division of a coding tree block into coding blocks isa partitioning. A coding tree block (CTB) may be defined as an N×N blockof samples for some value of N such that the division of a componentinto coding tree blocks is a partitioning. A coding tree unit (CTU) maybe defined as a coding tree block of luma samples, two correspondingcoding tree blocks of chroma samples of a picture that has three samplearrays, or a coding tree block of samples of a monochrome picture or apicture that is coded using three separate color planes and syntaxstructures used to code the samples. A coding unit (CU) may be definedas a coding block of luma samples, two corresponding coding blocks ofchroma samples of a picture that has three sample arrays, or a codingblock of samples of a monochrome picture or a picture that is codedusing three separate color planes and syntax structures used to code thesamples.

In some video codecs, such as High Efficiency Video Coding (HEVC) codec,video pictures are divided into coding units (CU) covering the area ofthe picture. A CU consists of one or more prediction units (PU) definingthe prediction process for the samples within the CU and one or moretransform units (TU) defining the prediction error coding process forthe samples in the said CU. Typically, a CU consists of a square blockof samples with a size selectable from a predefined set of possible CUsizes. A CU with the maximum allowed size may be named as LCU (largestcoding unit) or coding tree unit (CTU) and the video picture is dividedinto non-overlapping LCUs. An LCU can be further split into acombination of smaller CUs, e.g. by recursively splitting the LCU andresultant CUs. Each resulting CU typically has at least one PU and atleast one TU associated with it. Each PU and TU can be further splitinto smaller PUs and TUs in order to increase granularity of theprediction and prediction error coding processes, respectively. Each PUhas prediction information associated with it defining what kind of aprediction is to be applied for the pixels within that PU (e.g. motionvector information for inter predicted PUs and intra predictiondirectionality information for intra predicted PUs).

Each TU can be associated with information describing the predictionerror decoding process for the samples within the said TU (includinge.g. DCT coefficient information). It is typically signalled at CU levelwhether prediction error coding is applied or not for each CU. In thecase there is no prediction error residual associated with the CU, itcan be considered there are no TUs for the said CU. The division of theimage into CUs, and division of CUs into PUs and TUs is typicallysignalled in the bitstream allowing the decoder to reproduce theintended structure of these units.

In the HEVC standard, a picture can be partitioned in tiles, which arerectangular and contain an integer number of CTUs. In the HEVC standard,the partitioning to tiles forms a grid that may be characterized by alist of tile column widths (in CTUs) and a list of tile row heights (inCTUs). Tiles are ordered in the bitstream consecutively in the rasterscan order of the tile grid. A tile may contain an integer number ofslices.

In the HEVC, a slice consists of an integer number of CTUs. The CTUs arescanned in the raster scan order of CTUs within tiles or within apicture, if tiles are not in use. A slice may contain an integer numberof tiles or a slice can be contained in a tile. Within a CTU, the CUshave a specific scan order.

In HEVC, a slice may be defined as an integer number of coding treeunits contained in one independent slice segment and all subsequentdependent slice segments (if any) that precede the next independentslice segment (if any) within the same access unit. An independent slicesegment may be defined as a slice segment for which the values of thesyntax elements of the slice segment header are not inferred from thevalues for a preceding slice segment. A dependent slice segment may bedefined as a slice segment for which the values of some syntax elementsof the slice segment header are inferred from the values for thepreceding independent slice segment in decoding order. In other words,only the independent slice segment may have a “full” slice header. Anindependent slice segment may be conveyed in one NAL unit (without otherslice segments in the same NAL unit) and likewise a dependent slicesegment may be conveyed in one NAL unit (without other slice segments inthe same NAL unit).

In HEVC, a coded slice segment may be considered to comprise a slicesegment header and slice segment data. A slice segment header may bedefined as part of a coded slice segment containing the data elementspertaining to the first or all coding tree units represented in theslice segment. A slice header may be defined as the slice segment headerof the independent slice segment that is a current slice segment or themost recent independent slice segment that precedes a current dependentslice segment in decoding order. Slice segment data may comprise aninteger number of coding tree unit syntax structures.

In H.264/AVC and HEVC, in-picture prediction may be disabled acrossslice boundaries. Thus, slices can be regarded as a way to split a codedpicture into independently decodable pieces, and slices are thereforeoften regarded as elementary units for transmission. In many cases,encoders may indicate in the bitstream which types of in-pictureprediction are turned off across slice boundaries, and the decoderoperation takes this information into account for example whenconcluding which prediction sources are available. For example, samplesfrom a neighboring macroblock or CU may be regarded as unavailable forintra prediction, if the neighboring macroblock or CU resides in adifferent slice.

The elementary unit for the output of an H.264/AVC or HEVC encoder andthe input of an H.264/AVC or HEVC decoder, respectively, is a NetworkAbstraction Layer (NAL) unit. For transport over packet-orientednetworks or storage into structured files, NAL units may be encapsulatedinto packets or similar structures.

A NAL unit may be defined as a syntax structure containing an indicationof the type of data to follow and bytes containing that data in the formof an RBSP interspersed as necessary with emulation prevention bytes. Araw byte sequence payload (RBSP) may be defined as a syntax structurecontaining an integer number of bytes that is encapsulated in a NALunit. An RBSP is either empty or has the form of a string of data bitscontaining syntax elements followed by an RBSP stop bit and followed byzero or more subsequent bits equal to 0.

NAL units consist of a header and payload. In H.264/AVC, the NAL unitheader indicates the type of the NAL unit and whether a coded slicecontained in the NAL unit is a part of a reference picture or anon-reference picture. H.264/AVC includes a 2-bit nal_ref_idc syntaxelement, which when equal to 0 indicates that a coded slice contained inthe NAL unit is a part of a non-reference picture and when greater than0 indicates that a coded slice contained in the NAL unit is a part of areference picture. The NAL unit header for SVC and MVC NAL units mayadditionally contain various indications related to the scalability andmultiview hierarchy.

In HEVC, a two-byte NAL unit header is used for all specified NAL unittypes. The NAL unit header contains one reserved bit, a six-bit NAL unittype indication (called nal_unit_type), a six-bit reserved field (callednuh_layer_id) and a three-bit temporal_id_plus1 indication for temporallevel. The temporal_id_plus1 syntax element may be regarded as atemporal identifier for the NAL unit, and a zero-based TemporalIdvariable may be derived as follows: TemporalId=temporal_id_plus1−1.TemporalId equal to 0 corresponds to the lowest temporal level. Thevalue of temporal_id_plus1 is required to be non-zero in order to avoidstart code emulation involving the two NAL unit header bytes. Thebitstream created by excluding all VCL NAL units having a TemporalIdgreater than or equal to a selected value and including all other VCLNAL units remains conforming. Consequently, a picture having TemporalIdequal to TID does not use any picture having a TemporalId greater thanTID as inter prediction reference. A sub-layer or a temporal sub-layermay be defined to be a temporal scalable layer of a temporal scalablebitstream, consisting of VCL NAL units with a particular value of theTemporalId variable and the associated non-VCL NAL units. Without lossof generality, in some example embodiments a variable LayerId is derivedfrom the value of nuh_layer_id for example as follows:LayerId=nuh_layer_id. In the following, layer identifier, LayerId,nuh_layer_id and layer_id are used interchangeably unless otherwiseindicated.

In HEVC extensions nuh_layer_id and/or similar syntax elements in NALunit header carries scalability layer information. For example, theLayerId value nuh_layer_id and/or similar syntax elements may be mappedto values of variables or syntax elements describing differentscalability dimensions.

NAL units can be categorized into Video Coding Layer (VCL) NAL units andnon-VCL NAL units. VCL NAL units are typically coded slice NAL units. InH.264/AVC, coded slice NAL units contain syntax elements representingone or more coded macroblocks, each of which corresponds to a block ofsamples in the uncompressed picture. In HEVC, coded slice NAL unitscontain syntax elements representing one or more CU.

A non-VCL NAL unit may be for example one of the following types: asequence parameter set, a picture parameter set, a supplementalenhancement information (SEI) NAL unit, an access unit delimiter, an endof sequence NAL unit, an end of bitstream NAL unit, or a filler data NALunit. Parameter sets may be needed for the reconstruction of decodedpictures, whereas many of the other non-VCL NAL units are not necessaryfor the reconstruction of decoded sample values.

Parameters that remain unchanged through a coded video sequence may beincluded in a sequence parameter set. Examples of parameters that arerequired to be unchanged within a coded video sequence in many codingsystems and hence included in a sequence parameter set are the width andheight of the pictures included in the coded video sequence. In additionto the parameters that may be needed by the decoding process, thesequence parameter set may optionally contain video usabilityinformation (VUI), which includes parameters that may be important forbuffering, picture output timing, rendering, and resource reservation.In HEVC a sequence parameter set RBSP includes parameters that can bereferred to by one or more picture parameter set RBSPs or one or moreSEI NAL units containing a buffering period SEI message. A pictureparameter set contains such parameters that are likely to be unchangedin several coded pictures. A picture parameter set RBSP may includeparameters that can be referred to by the coded slice NAL units of oneor more coded pictures.

In HEVC, a video parameter set (VPS) may be defined as a syntaxstructure containing syntax elements that apply to zero or more entirecoded video sequences as determined by the content of a syntax elementfound in the SPS referred to by a syntax element found in the PPSreferred to by a syntax element found in each slice segment header. Avideo parameter set RBSP may include parameters that can be referred toby one or more sequence parameter set RBSPs.

The relationship and hierarchy between video parameter set (VPS),sequence parameter set (SPS), and picture parameter set (PPS) may bedescribed as follows. VPS resides one level above SPS in the parameterset hierarchy and in the context of scalability and/or 3D video. VPS mayinclude parameters that are common for all slices across all(scalability or view) layers in the entire coded video sequence. SPSincludes the parameters that are common for all slices in a particular(scalability or view) layer in the entire coded video sequence, and maybe shared by multiple (scalability or view) layers. PPS includes theparameters that are common for all slices in a particular layerrepresentation (the representation of one scalability or view layer inone access unit) and are likely to be shared by all slices in multiplelayer representations.

VPS may provide information about the dependency relationships of thelayers in a bitstream, as well as many other information that areapplicable to all slices across all (scalability or view) layers in theentire coded video sequence. VPS may be considered to comprise twoparts, the base VPS and a VPS extension, where the VPS extension may beoptionally present.

A SEI NAL unit may contain one or more SEI messages, which are notrequired for the decoding of output pictures but may assist in relatedprocesses, such as picture output timing, rendering, error detection,error concealment, and resource reservation. Several SEI messages arespecified in H.264/AVC and HEVC, and the user data SEI messages enableorganizations and companies to specify SEI messages for their own use.H.264/AVC and HEVC contain the syntax and semantics for the specifiedSEI messages but no process for handling the messages in the recipientis defined. Consequently, encoders are required to follow the H.264/AVCstandard or the HEVC standard when they create SEI messages, anddecoders conforming to the H.264/AVC standard or the HEVC standard,respectively, are not required to process SEI messages for output orderconformance. One of the reasons to include the syntax and semantics ofSEI messages in H.264/AVC and HEVC is to allow different systemspecifications to interpret the supplemental information identically andhence interoperate. It is intended that system specifications canrequire the use of particular SEI messages both in the encoding end andin the decoding end, and additionally the process for handlingparticular SEI messages in the recipient can be specified.

In HEVC, there are two types of SEI NAL units, namely the suffix SEI NALunit and the prefix SEI NAL unit, having a different nal_unit_type valuefrom each other. The SEI message(s) contained in a suffix SEI NAL unitare associated with the VCL NAL unit preceding, in decoding order, thesuffix SEI NAL unit. The SEI message(s) contained in a prefix SEI NALunit are associated with the VCL NAL unit following, in decoding order,the prefix SEI NAL unit.

In HEVC, a coded picture may be defined as a coded representation of apicture containing all coding tree units of the picture. In HEVC, anaccess unit (AU) may be defined as a set of NAL units that areassociated with each other according to a specified classification rule,are consecutive in decoding order, and contain at most one picture withany specific value of nuh_layer_id. In addition to containing the VCLNAL units of the coded picture, an access unit may also contain non-VCLNAL units.

It may be required that coded pictures appear in certain order within anaccess unit. For example, a coded picture with nuh_layer_id equal tonuhLayerIdA may be required to precede, in decoding order, all codedpictures with nuh_layer_id greater than nuhLayerIdA in the same accessunit. An AU typically contains all the coded pictures that represent thesame output time and/or capturing time.

A bitstream may be defined as a sequence of bits, in the form of a NALunit stream or a byte stream, that forms the representation of codedpictures and associated data forming one or more coded video sequences.A first bitstream may be followed by a second bitstream in the samelogical channel, such as in the same file or in the same connection of acommunication protocol. An elementary stream (in the context of videocoding) may be defined as a sequence of one or more bitstreams. The endof the first bitstream may be indicated by a specific NAL unit, whichmay be referred to as the end of bitstream (EOB) NAL unit and which isthe last NAL unit of the bitstream.

A byte stream format has been specified in H.264/AVC and HEVC fortransmission or storage environments that do not provide framingstructures. The byte stream format separates NAL units from each otherby attaching a start code in front of each NAL unit. To avoid falsedetection of NAL unit boundaries, encoders run a byte-oriented startcode emulation prevention algorithm, which adds an emulation preventionbyte to the NAL unit payload if a start code would have occurredotherwise. In order to, for example, enable straightforward gatewayoperation between packet- and stream-oriented systems, start codeemulation prevention may always be performed regardless of whether thebyte stream format is in use or not. The bit order for the byte streamformat may be specified to start with the most significant bit (MSB) ofthe first byte, proceed to the least significant bit (LSB) of the firstbyte, followed by the MSB of the second byte, etc. The byte streamformat may be considered to consist of a sequence of byte stream NALunit syntax structures. Each byte stream NAL unit syntax structure maybe considered to comprise one start code prefix followed by one NAL unitsyntax structure, as well as trailing and/or heading padding bits and/orbytes.

A motion-constrained tile set (MCTS) is such a set of one or more tilesthat the inter prediction process is constrained in encoding such thatno sample value outside the motion-constrained tile set, and no samplevalue at a fractional sample position that is derived using one or moresample values outside the motion-constrained tile set, is used for interprediction of any sample within the motion-constrained tile set. An MCTSmay be required to be rectangular. Additionally, the encoding of an MCTSis constrained in a manner that motion vector candidates are not derivedfrom blocks outside the MCTS. This may be enforced by turning offtemporal motion vector prediction of HEVC, or by disallowing the encoderto use the TMVP candidate or any motion vector prediction candidatefollowing the TMVP candidate in the merge or AMVP candidate list for PUslocated directly left of the right tile boundary of the MCTS except thelast one at the bottom right of the MCTS.

Note that sample locations used in inter prediction may be saturated sothat a location that would be outside the picture otherwise is saturatedto point to the corresponding boundary sample of the picture. Hence, ifa tile boundary is also a picture boundary, motion vectors mayeffectively cross that boundary or a motion vector may effectively causefractional sample interpolation that would refer to a location outsidethat boundary, since the sample locations are saturated onto theboundary. However, if tiles may be re-located in a tile mergingoperation (see e.g. embodiments of the present invention), encodersgenerating MCTSs may apply motion constraints to all tile boundaries ofthe MCTS, including picture boundaries.

The temporal motion-constrained tile sets SEI message of HEVC can beused to indicate the presence of motion-constrained tile sets in thebitstream.

A motion-constrained picture is such that the inter prediction processis constrained in encoding such that no sample value outside thepicture, and no sample value at a fractional sample position that isderived using one or more sample values outside the picture, would beused for inter prediction of any sample within the picture and/or samplelocations used for prediction need not be saturated to be within pictureboundaries.

It may be considered that in stereoscopic or two-view video, one videosequence or view is presented for the left eye while a parallel view ispresented for the right eye. More than two parallel views may be neededfor applications which enable viewpoint switching or forautostereoscopic displays which may present a large number of viewssimultaneously and let the viewers to observe the content from differentviewpoints.

A view may be defined as a sequence of pictures representing one cameraor viewpoint. The pictures representing a view may also be called viewcomponents. In other words, a view component may be defined as a codedrepresentation of a view in a single access unit. In multiview videocoding, more than one view are coded in a bitstream. Since views aretypically intended to be displayed on stereoscopic or multiviewautostereoscopic display or to be used for other 3D arrangements, theytypically represent the same scene and are content-wise partlyoverlapping although representing different viewpoints to the content.Hence, inter-view prediction may be utilized in multiview video codingto take advantage of inter-view correlation and improve compressionefficiency. One way to realize inter-view prediction is to include oneor more decoded pictures of one or more other views in the referencepicture list(s) of a picture being coded or decoded residing within afirst view. View scalability may refer to such multiview video coding ormultiview video bitstreams, which enable removal or omission of one ormore coded views, while the resulting bitstream remains conforming andrepresents video with a smaller number of views than originally.

Frame packing may be defined to comprise arranging more than one inputpicture, which may be referred to as (input) constituent frames, into anoutput picture. In general, frame packing is not limited to anyparticular type of constituent frames or the constituent frames need nothave a particular relation with each other. In many cases, frame packingis used for arranging constituent frames of a stereoscopic video clipinto a single picture sequence, as explained in more details in the nextparagraph. The arranging may include placing the input pictures inspatially non-overlapping areas within the output picture. For example,in a side-by-side arrangement, two input pictures are placed within anoutput picture horizontally adjacently to each other. The arranging mayalso include partitioning of one or more input pictures into two or moreconstituent frame partitions and placing the constituent framepartitions in spatially non-overlapping areas within the output picture.The output picture or a sequence of frame-packed output pictures may beencoded into a bitstream e.g. by a video encoder. The bitstream may bedecoded e.g. by a video decoder. The decoder or a post-processingoperation after decoding may extract the decoded constituent frames fromthe decoded picture(s) e.g. for displaying.

In frame-compatible stereoscopic video (a.k.a. frame packing ofstereoscopic video), a spatial packing of a stereo pair into a singleframe is performed at the encoder side as a pre-processing step forencoding and then the frame-packed frames are encoded with aconventional 2D video coding scheme. The output frames produced by thedecoder contain constituent frames of a stereo pair.

In a typical operation mode, the spatial resolution of the originalframes of each view and the packaged single frame have the sameresolution. In this case the encoder downsamples the two views of thestereoscopic video before the packing operation. The spatial packing mayuse for example a side-by-side or top-bottom format, and thedownsampling should be performed accordingly.

A uniform resource identifier (URI) may be defined as a string ofcharacters used to identify a name of a resource. Such identificationenables interaction with representations of the resource over a network,using specific protocols. A URI is defined through a scheme specifying aconcrete syntax and associated protocol for the URI. The uniformresource locator (URL) and the uniform resource name (URN) are forms ofURI. A URL may be defined as a URI that identifies a web resource andspecifies the means of acting upon or obtaining the representation ofthe resource, specifying both its primary access mechanism and networklocation. A URN may be defined as a URI that identifies a resource byname in a particular namespace. A URN may be used for identifying aresource without implying its location or how to access it. The termrequesting locator may be defined to an identifier that can be used torequest a resource, such as a file or a segment. A requesting locatormay, for example, be a URL or specifically an HTTP URL. A client may usea requesting locator with a communication protocol, such as HTTP, torequest a resource from a server or a sender.

Available media file format standards include ISO base media file format(ISO/IEC 14496-12, which may be abbreviated ISOBMFF), MPEG-4 file format(ISO/IEC 14496-14, also known as the MP4 format), file format for NALunit structured video (ISO/IEC 14496-15) and 3GPP file format (3GPP TS26.244, also known as the 3GP format). ISOBMFF is the base forderivation of all the above mentioned file formats (excluding theISOBMFF itself).

Some concepts, structures, and specifications of ISOBMFF are describedbelow as an example of a container file format, based on which someembodiments may be implemented. The aspects of the invention are notlimited to ISOBMFF, but rather the description is given for one possiblebasis on top of which the invention may be partly or fully realized.

A basic building block in the ISO base media file format is called abox. Each box has a header and a payload. The box header indicates thetype of the box and the size of the box in terms of bytes. A box mayenclose other boxes, and the ISO file format specifies which box typesare allowed within a box of a certain type. Furthermore, the presence ofsome boxes may be mandatory in each file, while the presence of otherboxes may be optional. Additionally, for some box types, it may beallowable to have more than one box present in a file. Thus, the ISObase media file format may be considered to specify a hierarchicalstructure of boxes.

According to the ISO family of file formats, a file includes media dataand metadata that are encapsulated into boxes. Each box is identified bya four character code (4CC) and starts with a header which informs aboutthe type and size of the box.

In files conforming to the ISO base media file format, the media datamay be provided in a media data ‘mdat’ box and the movie ‘moov’ box maybe used to enclose the metadata. In some cases, for a file to beoperable, both of the ‘mdat’ and ‘moov’ boxes may be required to bepresent. The movie ‘moov’ box may include one or more tracks, and eachtrack may reside in one corresponding track ‘trak’ box. A track may beone of the many types, including a media track that refers to samplesformatted according to a media compression format (and its encapsulationto the ISO base media file format). A track may be regarded as a logicalchannel.

Movie fragments may be used e.g. when recording content to ISO filese.g. in order to avoid losing data if a recording application crashes,runs out of memory space, or some other incident occurs. Without moviefragments, data loss may occur because the file format may require thatall metadata, e.g., the movie box, be written in one contiguous area ofthe file. Furthermore, when recording a file, there may not besufficient amount of memory space (e.g., random access memory RAM) tobuffer a movie box for the size of the storage available, andre-computing the contents of a movie box when the movie is closed may betoo slow. Moreover, movie fragments may enable simultaneous recordingand playback of a file using a regular ISO file parser. Furthermore, asmaller duration of initial buffering may be required for progressivedownloading, e.g., simultaneous reception and playback of a file whenmovie fragments are used and the initial movie box is smaller comparedto a file with the same media content but structured without moviefragments.

The movie fragment feature may enable splitting the metadata thatotherwise might reside in the movie box into multiple pieces. Each piecemay correspond to a certain period of time of a track. In other words,the movie fragment feature may enable interleaving file metadata andmedia data. Consequently, the size of the movie box may be limited andthe use cases mentioned above be realized.

In some examples, the media samples for the movie fragments may residein an mdat box. For the metadata of the movie fragments, however, a moofbox may be provided. The moof box may include the information for acertain duration of playback time that would previously have been in themoov box. The moov box may still represent a valid movie on its own, butin addition, it may include an mvex box indicating that movie fragmentswill follow in the same file. The movie fragments may extend thepresentation that is associated to the moov box in time.

Within the movie fragment there may be a set of track fragments,including anywhere from zero to a plurality per track. The trackfragments may in turn include anywhere from zero to a plurality of trackruns, each of which document is a contiguous run of samples for thattrack (and hence are similar to chunks). Within these structures, manyfields are optional and can be defaulted. The metadata that may beincluded in the moof box may be limited to a subset of the metadata thatmay be included in a moov box and may be coded differently in somecases. Details regarding the boxes that can be included in a moof boxmay be found from the ISOBMFF specification. A self-contained moviefragment may be defined to consist of a moof box and an mdat box thatare consecutive in the file order and where the mdat box contains thesamples of the movie fragment (for which the moof box provides themetadata) and does not contain samples of any other movie fragment (i.e.any other moof box).

The track reference mechanism can be used to associate tracks with eachother. The TrackReferenceBox includes box(es), each of which provides areference from the containing track to a set of other tracks. Thesereferences are labeled through the box type (i.e. the four-charactercode of the box) of the contained box(es).

The ISO Base Media File Format contains three mechanisms for timedmetadata that can be associated with particular samples: sample groups,timed metadata tracks, and sample auxiliary information. Derivedspecification may provide similar functionality with one or more ofthese three mechanisms.

A sample grouping in the ISO base media file format and its derivatives,such as the AVC file format and the SVC file format, may be defined asan assignment of each sample in a track to be a member of one samplegroup, based on a grouping criterion. A sample group in a samplegrouping is not limited to being contiguous samples and may containnon-adjacent samples. As there may be more than one sample grouping forthe samples in a track, each sample grouping may have a type field toindicate the type of grouping. Sample groupings may be represented bytwo linked data structures: (1) a SampleToGroupBox (sbgp box) representsthe assignment of samples to sample groups; and (2) aSampleGroupDescriptionBox (sgpd box) contains a sample group entry foreach sample group describing the properties of the group. There may bemultiple instances of the SampleToGroupBox and SampleGroupDescriptionBoxbased on different grouping criteria. These may be distinguished by atype field used to indicate the type of grouping. SampleToGroupBox maycomprise a grouping_type_parameter field that can be used e.g. toindicate a sub-type of the grouping.

The restricted video (‘resv’) sample entry and mechanism has beenspecified for the ISOBMFF in order to handle situations where the fileauthor requires certain actions on the player or renderer after decodingof a visual track. Players not recognizing or not capable of processingthe required actions are stopped from decoding or rendering therestricted video tracks. The ‘resv’ sample entry mechanism applies toany type of video codec. A RestrictedSchemeInfoBox is present in thesample entry of ‘resv’ tracks and comprises a OriginalFormatBox,SchemeTypeBox, and SchemeInformationBox. The original sample entry typethat would have been unless the ‘resv’ sample entry type were used iscontained in the OriginalFormatBox. The SchemeTypeBox provides anindication which type of processing is required in the player to processthe video. The SchemeInformationBox comprises further information of therequired processing. The scheme type may impose requirements on thecontents of the SchemeInformationBox. For example, the stereo videoscheme indicated in the SchemeTypeBox indicates that when decoded frameseither contain a representation of two spatially packed constituentframes that form a stereo pair (frame packing) or only one view of astereo pair (left and right views in different tracks). StereoVideoBoxmay be contained in SchemeInformationBox to provide further informatione.g. on which type of frame packing arrangement has been used (e.g.side-by-side or top-bottom).

The Matroska file format is capable of (but not limited to) storing anyof video, audio, picture, or subtitle tracks in one file. Matroska maybe used as a basis format for derived file formats, such as WebM.Matroska uses Extensible Binary Meta Language (EBML) as basis. EBMLspecifies a binary and octet (byte) aligned format inspired by theprinciple of XML. EBML itself is a generalized description of thetechnique of binary markup. A Matroska file consists of Elements thatmake up an EBML “document.” Elements incorporate an Element ID, adescriptor for the size of the element, and the binary data itselfElements can be nested. A Segment Element of Matroska is a container forother top-level (level 1) elements. A Matroska file may comprise (but isnot limited to be composed of) one Segment. Multimedia data in Matroskafiles is organized in Clusters (or Cluster Elements), each containingtypically a few seconds of multimedia data. A Cluster comprisesBlockGroup elements, which in turn comprise Block Elements. A CuesElement comprises metadata which may assist in random access or seekingand may include file pointers or respective timestamps for seek points.

Several commercial solutions for adaptive streaming over HTTP, such asMicrosoft® Smooth Streaming, Apple® Adaptive HTTP Live Streaming andAdobe® Dynamic Streaming, have been launched as well as standardizationprojects have been carried out. Adaptive HTTP streaming (AHS) was firststandardized in Release 9 of 3rd Generation Partnership Project (3GPP)packet-switched streaming (PSS) service (3GPP TS 26.234 Release 9:“Transparent end-to-end packet-switched streaming service (PSS);protocols and codecs”). MPEG took 3GPP AHS Release 9 as a starting pointfor the MPEG DASH standard (ISO/IEC 23009-1: “Dynamic adaptive streamingover HTTP (DASH)-Part 1: Media presentation description and segmentformats,” International Standard, 2^(nd) Edition, 2014). MPEG DASH and3GP-DASH are technically close to each other and may therefore becollectively referred to as DASH. Some concepts, formats, and operationsof DASH are described below as an example of a video streaming system,wherein the embodiments may be implemented. The aspects of the inventionare not limited to DASH, but rather the description is given for onepossible basis on top of which the invention may be partly or fullyrealized.

In DASH, the multimedia content may be stored on an HTTP server and maybe delivered using HTTP. The content may be stored on the server in twoparts: Media Presentation Description (MPD), which describes a manifestof the available content, its various alternatives, their URL addresses,and other characteristics; and segments, which contain the actualmultimedia bitstreams in the form of chunks, in a single or multiplefiles. The MDP provides the necessary information for clients toestablish a dynamic adaptive streaming over HTTP. The MPD containsinformation describing media presentation, such as an HTTP-uniformresource locator (URL) of each Segment to make GET Segment request. Toplay the content, the DASH client may obtain the MPD e.g. by using HTTP,email, thumb drive, broadcast, or other transport methods. By parsingthe MPD, the DASH client may become aware of the program timing,media-content availability, media types, resolutions, minimum andmaximum bandwidths, and the existence of various encoded alternatives ofmultimedia components, accessibility features and required digitalrights management (DRM), media-component locations on the network, andother content characteristics. Using this information, the DASH clientmay select the appropriate encoded alternative and start streaming thecontent by fetching the segments using e.g. HTTP GET requests. Afterappropriate buffering to allow for network throughput variations, theclient may continue fetching the subsequent segments and also monitorthe network bandwidth fluctuations. The client may decide how to adaptto the available bandwidth by fetching segments of differentalternatives (with lower or higher bitrates) to maintain an adequatebuffer.

In DASH, hierarchical data model is used to structure media presentationas shown in FIG. 7 a . A media presentation consists of a sequence ofone or more Periods, each Period contains one or more Groups, each Groupcontains one or more Adaptation Sets, each Adaptation Sets contains oneor more Representations, each Representation consists of one or moreSegments. A Representation is one of the alternative choices of themedia content or a subset thereof typically differing by the encodingchoice, e.g. by bitrate, resolution, language, codec, etc. The Segmentcontains certain duration of media data, and metadata to decode andpresent the included media content. A Segment is identified by a URI andcan typically be requested by a HTTP GET request. A Segment may bedefined as a unit of data associated with an HTTP-URL and optionally abyte range that are specified by an MPD.

The DASH MPD complies with Extensible Markup Language (XML) and istherefore specified through elements and attributes as defined in XML.The MPD may be specified using the following conventions: Elements in anXML document may be identified by an upper-case first letter and mayappear in bold face as Element. To express that an element Element1 iscontained in another element Element2, one may write Element2.Element1.If an element's name consists of two or more combined words,camel-casing may be used, e.g. ImportantElement. Elements may be presenteither exactly once, or the minimum and maximum occurrence may bedefined by <minOccurs> . . . <maxOccurs>. Attributes in an XML documentmay be identified by a lower-case first letter as well as they may bepreceded by a ‘@’-sign, e.g. @attribute. To point to a specificattribute @attribute contained in an element Element, one may writeElement@attribute. If an attribute's name consists of two or morecombined words, camel-casing may be used after the first word, e.g.@veryImportantAttribute. Attributes may have assigned a status in theXML as mandatory (M), optional (O), optional with default value (OD) andconditionally mandatory (CM).

In DASH, an independent representation may be defined as arepresentation that can be processed independently of any otherrepresentations. An independent representation may be understood tocomprise an independent bitstream or an independent layer of abitstream. A dependent representation may be defined as a representationfor which Segments from its complementary representations are necessaryfor presentation and/or decoding of the contained media contentcomponents. A dependent representation may be understood to comprisee.g. a predicted layer of a scalable bitstream. A complementaryrepresentation may be defined as a representation which complements atleast one dependent representation. A complementary representation maybe an independent representation or a dependent representation.Dependent Representations may be described by a Representation elementthat contains a @dependencyId attribute. Dependent Representations canbe regarded as regular Representations except that they depend on a setof complementary Representations for decoding and/or presentation. The@dependencyId contains the values of the @id attribute of all thecomplementary Representations, i.e. Representations that are necessaryto present and/or decode the media content components contained in thisdependent Representation.

In the context of DASH, the following definitions may be used: A mediacontent component or a media component may be defined as one continuouscomponent of the media content with an assigned media component typethat can be encoded individually into a media stream. Media content maybe defined as one media content period or a contiguous sequence of mediacontent periods. Media content component type may be defined as a singletype of media content such as audio, video, or text. A media stream maybe defined as an encoded version of a media content component.

An Initialization Segment may be defined as a Segment containingmetadata that is necessary to present the media streams encapsulated inMedia Segments. In ISOBMFF based segment formats, an InitializationSegment may comprise the Movie Box (‘moov’) which might not includemetadata for any samples, i.e. any metadata for samples is provided in‘moof’ boxes.

A Media Segment contains certain duration of media data for playback ata normal speed, such duration is referred as Media Segment duration orSegment duration. The content producer or service provider may selectthe Segment duration according to the desired characteristics of theservice. For example, a relatively short Segment duration may be used ina live service to achieve a short end-to-end latency. The reason is thatSegment duration is typically a lower bound on the end-to-end latencyperceived by a DASH client since a Segment is a discrete unit ofgenerating media data for DASH. Content generation is typically donesuch a manner that a whole Segment of media data is made available for aserver. Furthermore, many client implementations use a Segment as theunit for GET requests. Thus, in typical arrangements for live services aSegment can be requested by a DASH client only when the whole durationof Media Segment is available as well as encoded and encapsulated into aSegment. For on-demand service, different strategies of selectingSegment duration may be used.

DASH supports rate adaptation by dynamically requesting Media Segmentsfrom different Representations within an Adaptation Set to match varyingnetwork bandwidth. When a DASH client switches up/down Representation,coding dependencies within Representation have to be taken into account.A Representation switch may only happen at a random access point (RAP),which is typically used in video coding techniques such as H.264/AVC. InDASH, a more general concept named Stream Access Point (SAP) isintroduced to provide a codec-independent solution for accessing aRepresentation and switching between Representations. In DASH, a SAP isspecified as a position in a Representation that enables playback of amedia stream to be started using only the information contained inRepresentation data starting from that position onwards (preceded byinitialising data in the Initialisation Segment, if any). Hence,Representation switching can be performed in SAP.

Several types of SAP have been specified, including the following. SAPType 1 corresponds to what is known in some coding schemes as a “ClosedGOP random access point” (in which all pictures, in decoding order, canbe correctly decoded, resulting in a continuous time sequence ofcorrectly decoded pictures with no gaps) and in addition the firstpicture in decoding order is also the first picture in presentationorder. SAP Type 2 corresponds to what is known in some coding schemes asa “Closed GOP random access point” (in which all pictures, in decodingorder, can be correctly decoded, resulting in a continuous time sequenceof correctly decoded pictures with no gaps), for which the first picturein decoding order may not be the first picture in presentation order.SAP Type 3 corresponds to what is known in some coding schemes as an“Open GOP random access point”, in which there may be some pictures indecoding order that cannot be correctly decoded and have presentationtimes earlier than intra-coded picture associated with the SAP.

A stream access point (SAP) sample group as specified in ISOBMFFidentifies samples as being of the indicated SAP type. Thegrouping_type_parameter for the SAP sample group comprises the fieldstarget_layers and layer_id_method_idc. target_layers specifies thetarget_layers for the indicated SAPs. The semantics of target_layers maydepend on the value of layer_id_method_idc, which specifies thesemantics of target_layers. layer_id_method_idc equal to 0 specifiesthat the target_layers consist of all the layers represented by thetrack. The sample group description entry for the SAP sample groupcomprises the fields dependent_flag and SAP_type. dependent_flag may berequired to be 0 for non-layered media. dependent_flag equal to 1specifies that the reference layers, if any, for predicting the targetlayers may have to be decoded for accessing a sample of this samplegroup. dependent_flag equal to 0 specifies that the reference layers, ifany, for predicting the target layers need not be decoded for accessingany SAP of this sample group. sap type values in the range of 1 to 6,inclusive, specify the SAP type, of the associated samples.

A sync sample may be defined as a sample in a track that is of a SAP oftype 1 or 2. Sync samples may be indicated with SyncSampleBox or bysample_is_non_sync_sample equal to 0 in the signaling for trackfragments.

A Segment may further be partitioned into Subsegments e.g. to enabledownloading segments in multiple parts. Subsegments may be required tocontain complete access units. Subsegments may be indexed by SegmentIndex box, which contains information to map presentation time range andbyte range for each Subsegment. The Segment Index box may also describesubsegments and stream access points in the segment by signaling theirdurations and byte offsets. A DASH client may use the informationobtained from Segment Index box(es) to make a HTTP GET request for aspecific Subsegment using byte range HTTP request. If relatively longSegment duration is used, then Subsegments may be used to keep the sizeof HTTP responses reasonable and flexible for bitrate adaptation. Theindexing information of a segment may be put in the single box at thebeginning of that segment, or spread among many indexing boxes in thesegment. Different methods of spreading are possible, such ashierarchical, daisy chain, and hybrid. This technique may avoid adding alarge box at the beginning of the segment and therefore may prevent apossible initial download delay.

It may be required that for any dependent Representation X that dependson complementary Representation Y, the m-th Subsegment of X and the n-thSubsegment of Y shall be non-overlapping whenever m is not equal to n.It may be required that for dependent Representations the concatenationof the Initialization Segment with the sequence of Subsegments of thedependent Representations, each being preceded by the correspondingSubsegment of each of the complementary Representations in order asprovided in the @dependencyId attribute shall represent a conformingSubsegment sequence conforming to the media format as specified in the@mimeType attribute for this dependent Representation.

MPEG-DASH defines segment-container formats for both ISOBMFF and MPEG-2Transport Streams. Other specifications may specify segment formatsbased on other container formats. For example, a segment format based onMatroska container file format has been proposed and may be summarizedas follows. When Matroska files are carried as DASH segments or alike,the association of DASH units and Matroska units may be specified asfollows. A subsegment (of DASH) may be defined as one or moreconsecutive Clusters of Matroska-encapsulated content. An InitializationSegment of DASH may be required to comprise the EBML header, Segmentheader (of Matroska), Segment Information (of Matroska) and Tracks, andmay optionally comprise other level1 elements and padding. A SegmentIndex of DASH may comprise a Cues Element of Matroska.

FIG. 7 b shows an example of an omnidirectional streaming system 600.Raw video signal may be input 601 and motion constrained encoding 602may be applied to the raw video data. The encoded image information maybe capsulated to one or more files and stored 603. The file(s) may besegmented 604 e.g. to comply with a segment format of MPEG DASH, andMedia Presentation Description may be formed 605. The content may bedelivered 606 via a communication network to a player e.g. as a responseto a request from the player. In the player the received segments areparsed and file(s) decapsulated 607 before decoding 608 and playback609.

A tile track may be defined as a track that contains sequences of one ormore motion-constrained tile sets of a coded bitstream. Decoding of atile track without the other tile tracks of the bitstream may require aspecialized decoder, which may be e.g. required to skip absent tiles inthe decoding process. An HEVC tile track specified in ISO/IEC 14496-15enables storage of one or more temporal motion-constrained tile sets asa track. When a tile track contains tiles of an HEVC base layer, thesample entry type ‘hvt1’ is used. When a tile track contains tiles of anon-base layer, the sample entry type ‘lht1’ is used. A sample of a tiletrack consists of one or more complete tiles in one or more completeslice segments. A tile track is independent from any other tile trackthat includes VCL NAL units of the same layer as this tile track. A tiletrack has a ‘tbas’ track reference to a tile base track. The tile basetrack does not include VCL NAL units. A tile base track indicates thetile ordering using a ‘sabt’ track reference to the tile tracks. An HEVCcoded picture corresponding to a sample in the tile base track can bereconstructed by collecting the coded data from the tile-aligned samplesof the tracks indicated by the ‘sabt’ track reference in the order ofthe track references.

A constructed tile set track is a tile set track, e.g. a track accordingto ISOBMFF, containing constructors that, when executed, result into atile set bitstream.

A constructor is a set of instructions that, when executed, results intoa valid piece of sample data according to the underlying sample format.

An extractor is a constructor that, when executed, copies the sampledata of an indicated byte range of an indicated sample of an indicatedtrack. Inclusion by reference may be defined as an extractor or alikethat, when executed, copies the sample data of an indicated byte rangeof an indicated sample of an indicated track.

A full-picture-compliant tile set {track|bitstream} is a tile set{track|bitstream} that conforms to the full-picture {track|bitstream}format. Here, the notation {optionA|optionB} illustrates alternatives,i.e. either optionA or optionB, which is selected consistently in allselections. A full-picture-compliant tile set track can be played aswith any full-picture track using the parsing and decoding process offull-picture tracks. A full-picture-compliant bitstream can be decodedas with any full-picture bitstream using the decoding process offull-picture bitstreams. A full-picture track is a track representing anoriginal bitstream (including all its tiles). A tile set bitstream is abitstream that contains a tile set of an original bitstream but notrepresenting the entire original bitstream. A tile set track is a trackrepresenting a tile set of an original bitstream but not representingthe entire original bitstream.

A full-picture-compliant tile set track may comprise extractors asdefined for HEVC. An extractor may, for example, be an in-lineconstructor including a slice segment header and a sample constructorextracting coded video data for a tile set from a referencedfull-picture track.

An in-line constructor is a constructor that, when executed, returns thesample data that it contains. For example, an in-line constructor maycomprise a set of instructions for rewriting a new slice header. Thephrase in-line may be used to indicate coded data that is included inthe sample of a track.

A full-picture track is a track representing an original bitstream(including all its tiles).

A NAL-unit-like structure refers to a structure with the properties of aNAL unit except that start code emulation prevention is not performed.

A pre-constructed tile set track is a tile set track containing thesample data in-line.

A tile set bitstream is a bitstream that contains a tile set of anoriginal bitstream but not representing the entire original bitstream.

A tile set track is a track representing a tile set of an originalbitstream but not representing the entire original bitstream.

Video codec may comprise an encoder that transforms the input video intoa compressed representation suited for storage/transmission and adecoder that can uncompress the compressed video representation backinto a viewable form. A video encoder and/or a video decoder may also beseparate from each other, i.e. need not form a codec. Typically, encoderdiscards some information in the original video sequence in order torepresent the video in a more compact form (that is, at lower bitrate).A video encoder may be used to encode an image sequence, as definedsubsequently, and a video decoder may be used to decode a coded imagesequence. A video encoder or an intra coding part of a video encoder oran image encoder may be used to encode an image, and a video decoder oran inter decoding part of a video decoder or an image decoder may beused to decode a coded image.

Some hybrid video encoders, for example many encoder implementations ofITU-T H.263 and H.264, encode the video information in two phases.Firstly, pixel values in a certain picture area (or “block”) arepredicted for example by motion compensation means (finding andindicating an area in one of the previously coded video frames thatcorresponds closely to the block being coded) or by spatial means (usingthe pixel values around the block to be coded in a specified manner).Secondly the prediction error, i.e. the difference between the predictedblock of pixels and the original block of pixels, is coded. This istypically done by transforming the difference in pixel values using aspecified transform (e.g. Discrete Cosine Transform (DCT) or a variantof it), quantizing the coefficients and entropy coding the quantizedcoefficients. By varying the fidelity of the quantization process,encoder can control the balance between the accuracy of the pixelrepresentation (picture quality) and size of the resulting coded videorepresentation (file size or transmission bitrate).

In temporal prediction, the sources of prediction are previously decodedpictures (a.k.a. reference pictures). In intra block copy (a.k.a.intra-block-copy prediction), prediction is applied similarly totemporal prediction but the reference picture is the current picture andonly previously decoded samples can be referred in the predictionprocess. Inter-layer or inter-view prediction may be applied similarlyto temporal prediction, but the reference picture is a decoded picturefrom another scalable layer or from another view, respectively. In somecases, inter prediction may refer to temporal prediction only, while inother cases inter prediction may refer collectively to temporalprediction and any of intra block copy, inter-layer prediction, andinter-view prediction provided that they are performed with the same orsimilar process than temporal prediction. Inter prediction or temporalprediction may sometimes be referred to as motion compensation ormotion-compensated prediction.

Intra prediction utilizes the fact that adjacent pixels within the samepicture are likely to be correlated. Intra prediction can be performedin spatial or transform domain, i.e., either sample values or transformcoefficients can be predicted. Intra prediction is typically exploitedin intra coding, where no inter prediction is applied.

There may be different types of intra prediction modes available in acoding scheme, out of which an encoder can select and indicate the usedone, e.g. on block or coding unit basis. A decoder may decode theindicated intra prediction mode and reconstruct the prediction blockaccordingly. For example, several angular intra prediction modes, eachfor different angular directions, may be available. Angular intraprediction may be considered to extrapolate the border samples ofadjacent blocks along a linear prediction direction. Additionally oralternatively, a planar prediction mode may be available. Planarprediction may be considered to essentially form a prediction block, inwhich each sample of a prediction block may be specified to be anaverage of the vertically aligned sample in the adjacent sample columnon the left of the current block and the horizontally aligned sample inthe adjacent sample line above the current block. Additionally oralternatively, a DC prediction mode may be available, in which theprediction block is essentially an average sample value of a neighboringblock or blocks.

One outcome of the coding procedure is a set of coding parameters, suchas motion vectors and quantized transform coefficients. Many parameterscan be entropy-coded more efficiently if they are predicted first fromspatially or temporally neighbouring parameters. For example, a motionvector may be predicted from spatially adjacent motion vectors and onlythe difference relative to the motion vector predictor may be coded.Prediction of coding parameters and intra prediction may be collectivelyreferred to as in-picture prediction.

FIG. 8 a shows a block diagram of a video encoder suitable for employingembodiments of the invention. FIG. 8 a presents an encoder for twolayers, but it would be appreciated that presented encoder could besimilarly simplified to encode only one layer or extended to encode morethan two layers. FIG. 8 a illustrates an embodiment of a video encodercomprising a first encoder section 500 for a base layer and a secondencoder section 502 for an enhancement layer. Each of the first encodersection 500 and the second encoder section 502 may comprise similarelements for encoding incoming pictures. The encoder sections 500, 502may comprise a pixel predictor 302, 402, prediction error encoder 303,403 and prediction error decoder 304, 404. FIG. 8 a also shows anembodiment of the pixel predictor 302, 402 as comprising aninter-predictor 306, 406, an intra-predictor 308, 408, a mode selector310, 410, a filter 316, 416, and a reference frame memory 318, 418. Thepixel predictor 302 of the first encoder section 500 receives 300 baselayer images of a video stream to be encoded at both the inter-predictor306 (which determines the difference between the image and a motioncompensated reference frame 318) and the intra-predictor 308 (whichdetermines a prediction for an image block based only on the alreadyprocessed parts of current frame or picture). The output of both theinter-predictor and the intra-predictor are passed to the mode selector310. The intra-predictor 308 may have more than one intra-predictionmodes. Hence, each mode may perform the intra-prediction and provide thepredicted signal to the mode selector 310. The mode selector 310 alsoreceives a copy of the base layer picture 300. Correspondingly, thepixel predictor 402 of the second encoder section 502 receives 400enhancement layer images of a video stream to be encoded at both theinter-predictor 406 (which determines the difference between the imageand a motion compensated reference frame 418) and the intra-predictor408 (which determines a prediction for an image block based only on thealready processed parts of current frame or picture). The output of boththe inter-predictor and the intra-predictor are passed to the modeselector 410. The intra-predictor 408 may have more than oneintra-prediction modes. Hence, each mode may perform theintra-prediction and provide the predicted signal to the mode selector410. The mode selector 410 also receives a copy of the enhancement layerpicture 400.

Depending on which encoding mode is selected to encode the currentblock, the output of the inter-predictor 306, 406 or the output of oneof the optional intra-predictor modes or the output of a surface encoderwithin the mode selector is passed to the output of the mode selector310, 410. The output of the mode selector is passed to a first summingdevice 321, 421. The first summing device may subtract the output of thepixel predictor 302, 402 from the base layer picture 300/enhancementlayer picture 400 to produce a first prediction error signal 320, 420which is input to the prediction error encoder 303, 403.

The pixel predictor 302, 402 further receives from a preliminaryreconstructor 339, 439 the combination of the prediction representationof the image block 312, 412 and the output 338, 438 of the predictionerror decoder 304, 404. The preliminary reconstructed image 314, 414 maybe passed to the intra-predictor 308, 408 and to a filter 316, 416. Thefilter 316, 416 receiving the preliminary representation may filter thepreliminary representation and output a final reconstructed image 340,440 which may be saved in a reference frame memory 318, 418. Thereference frame memory 318 may be connected to the inter-predictor 306to be used as the reference image against which a future base layerpicture 300 is compared in inter-prediction operations. Subject to thebase layer being selected and indicated to be source for inter-layersample prediction and/or inter-layer motion information prediction ofthe enhancement layer according to some embodiments, the reference framememory 318 may also be connected to the inter-predictor 406 to be usedas the reference image against which a future enhancement layer pictures400 is compared in inter-prediction operations. Moreover, the referenceframe memory 418 may be connected to the inter-predictor 406 to be usedas the reference image against which a future enhancement layer picture400 is compared in inter-prediction operations.

Filtering parameters from the filter 316 of the first encoder section500 may be provided to the second encoder section 502 subject to thebase layer being selected and indicated to be source for predicting thefiltering parameters of the enhancement layer according to someembodiments.

The prediction error encoder 303, 403 comprises a transform unit 342,442 and a quantizer 344, 444. The transform unit 342, 442 transforms thefirst prediction error signal 320, 420 to a transform domain. Thetransform is, for example, the DCT transform. The quantizer 344, 444quantizes the transform domain signal, e.g. the DCT coefficients, toform quantized coefficients.

The prediction error decoder 304, 404 receives the output from theprediction error encoder 303, 403 and performs the opposite processes ofthe prediction error encoder 303, 403 to produce a decoded predictionerror signal 338, 438 which, when combined with the predictionrepresentation of the image block 312, 412 at the second summing device339, 439, produces the preliminary reconstructed image 314, 414. Theprediction error decoder may be considered to comprise a dequantizer361, 461, which dequantizes the quantized coefficient values, e.g. DCTcoefficients, to reconstruct the transform signal and an inversetransformation unit 363, 463, which performs the inverse transformationto the reconstructed transform signal wherein the output of the inversetransformation unit 363, 463 contains reconstructed block(s). Theprediction error decoder may also comprise a block filter which mayfilter the reconstructed block(s) according to further decodedinformation and filter parameters.

The entropy encoder 330, 430 receives the output of the prediction errorencoder 303, 403 and may perform a suitable entropy encoding/variablelength encoding on the signal to provide error detection and correctioncapability. The outputs of the entropy encoders 330, 430 may be insertedinto a bitstream e.g. by a multiplexer 508.

FIG. 8 b shows a block diagram of a video decoder suitable for employingembodiments of the invention. FIG. 8 b depicts a structure of atwo-layer decoder, but it would be appreciated that the decodingoperations may similarly be employed in a single-layer decoder.

The video decoder 550 comprises a first decoder section 552 for baselayer pictures and a second decoder section 554 for enhancement layerpictures. Block 556 illustrates a demultiplexer for deliveringinformation regarding base layer pictures to the first decoder section552 and for delivering information regarding enhancement layer picturesto the second decoder section 554. Reference P′n stands for a predictedrepresentation of an image block. Reference D′n stands for areconstructed prediction error signal. Blocks 704, 804 illustratepreliminary reconstructed images (I′n). Reference R′n stands for a finalreconstructed image. Blocks 703, 803 illustrate inverse transform (T-1).Blocks 702, 802 illustrate inverse quantization (Q-1). Blocks 700, 800illustrate entropy decoding (E-1). Blocks 706, 806 illustrate areference frame memory (RFM). Blocks 707, 807 illustrate prediction (P)(either inter prediction or intra prediction). Blocks 708, 808illustrate filtering (F). Blocks 709, 809 may be used to combine decodedprediction error information with predicted base or enhancement layerpictures to obtain the preliminary reconstructed images (I′n).Preliminary reconstructed and filtered base layer pictures may be output710 from the first decoder section 552 and preliminary reconstructed andfiltered enhancement layer pictures may be output 810 from the seconddecoder section 554.

Herein, the decoder could be interpreted to cover any operational unitcapable to carry out the decoding operations, such as a player, areceiver, a gateway, a demultiplexer and/or a decoder.

The decoder reconstructs the output video by applying prediction meanssimilar to the encoder to form a predicted representation of the pixelblocks (using the motion or spatial information created by the encoderand stored in the compressed representation) and prediction errordecoding (inverse operation of the prediction error coding recoveringthe quantized prediction error signal in spatial pixel domain). Afterapplying prediction and prediction error decoding means the decoder sumsup the prediction and prediction error signals (pixel values) to formthe output video frame. The decoder (and encoder) can also applyadditional filtering means to improve the quality of the output videobefore passing it for display and/or storing it as prediction referencefor the forthcoming frames in the video sequence.

In typical video codecs the motion information is indicated with motionvectors associated with each motion compensated image block, such as aprediction unit. Each of these motion vectors represents thedisplacement of the image block in the picture to be coded (in theencoder side) or decoded (in the decoder side) and the prediction sourceblock in one of the previously coded or decoded pictures. In order torepresent motion vectors efficiently those are typically codeddifferentially with respect to block specific predicted motion vectors.In typical video codecs the predicted motion vectors are created in apredefined way, for example calculating the median of the encoded ordecoded motion vectors of the adjacent blocks. Another way to createmotion vector predictions is to generate a list of candidate predictionsfrom adjacent blocks and/or co-located blocks in temporal referencepictures and signalling the chosen candidate as the motion vectorpredictor. In addition to predicting the motion vector values, it can bepredicted which reference picture(s) are used for motion-compensatedprediction and this prediction information may be represented forexample by a reference index of previously coded/decoded picture. Thereference index is typically predicted from adjacent blocks and/orco-located blocks in temporal reference picture. Moreover, typical highefficiency video codecs employ an additional motion informationcoding/decoding mechanism, often called merging/merge mode, where allthe motion field information, which includes motion vector andcorresponding reference picture index for each available referencepicture list, is predicted and used without any modification/correction.Similarly, predicting the motion field information is carried out usingthe motion field information of adjacent blocks and/or co-located blocksin temporal reference pictures and the used motion field information issignalled among a list of motion field candidate list filled with motionfield information of available adjacent/co-located blocks.

Typical video codecs enable the use of uni-prediction, where a singleprediction block is used for a block being (de)coded, and bi-prediction,where two prediction blocks are combined to form the prediction for ablock being (de)coded. Some video codecs enable weighted prediction,where the sample values of the prediction blocks are weighted prior toadding residual information. For example, multiplicative weightingfactor and an additive offset which can be applied. In explicit weightedprediction, enabled by some video codecs, a weighting factor and offsetmay be coded for example in the slice header for each allowablereference picture index. In implicit weighted prediction, enabled bysome video codecs, the weighting factors and/or offsets are not codedbut are derived e.g. based on the relative picture order count (POC)distances of the reference pictures.

In typical video codecs the prediction residual after motioncompensation is first transformed with a transform kernel (like DCT) andthen coded. The reason for this is that often there still exists somecorrelation among the residual and transform can in many cases helpreduce this correlation and provide more efficient coding.

Typical video encoders utilize Lagrangian cost functions to find optimalcoding modes, e.g. the desired Macroblock mode and associated motionvectors. This kind of cost function uses a weighting factor λ to tietogether the (exact or estimated) image distortion due to lossy codingmethods and the (exact or estimated) amount of information that isrequired to represent the pixel values in an image area:C=D+λR  (1)

where C is the Lagrangian cost to be minimized, D is the imagedistortion (e.g. Mean Squared Error) with the mode and motion vectorsconsidered, and R the number of bits needed to represent the requireddata to reconstruct the image block in the decoder (including the amountof data to represent the candidate motion vectors).

H.264/AVC and HEVC include a concept of picture order count (POC). Avalue of POC is derived for each picture and is non-decreasing withincreasing picture position in output order. POC therefore indicates theoutput order of pictures. POC may be used in the decoding process, forexample, for implicit scaling of motion vectors in the temporal directmode of bi-predictive slices, for implicitly derived weights in weightedprediction, and for reference picture list initialization. Furthermore,POC may be used in the verification of output order conformance.

Video encoders and/or decoders may be able to store multiple referencepictures in a decoded picture buffer (DPB) and use them adaptively forinter prediction. The reference picture management may be defined as aprocess to determine which reference pictures are maintained in the DPB.Examples of reference picture management are described in the following.

In HEVC, a reference picture set (RPS) syntax structure and decodingprocess are used. A reference picture set valid or active for a pictureincludes all the reference pictures used as reference for the pictureand all the reference pictures that are kept marked as “used forreference” for any subsequent pictures in decoding order. There are sixsubsets of the reference picture set, which are referred to as namelyRefPicSetStCurr0 (a.k.a. RefPicSetStCurrBefore), RefPicSetStCurr1(a.k.a. RefPicSetStCurrAfter), RefPicSetStFoll0, RefPicSetStFoll1,RefPicSetLtCurr, and RefPicSetLtFoll. RefPicSetStFoll0 andRefPicSetStFoll1 may also be considered to form jointly one subsetRefPicSetStFoll. The notation of the six subsets is as follows. “Curr”refers to reference pictures that are included in the reference picturelists of the current picture and hence may be used as inter predictionreference for the current picture. “Foll” refers to reference picturesthat are not included in the reference picture lists of the currentpicture but may be used in subsequent pictures in decoding order asreference pictures. “St” refers to short-term reference pictures, whichmay generally be identified through a certain number of leastsignificant bits of their POC value. “Lt” refers to long-term referencepictures, which are specifically identified and generally have a greaterdifference of POC values relative to the current picture than what canbe represented by the mentioned certain number of least significantbits. “0” refers to those reference pictures that have a smaller POCvalue than that of the current picture. “1” refers to those referencepictures that have a greater POC value than that of the current picture.RefPicSetStCurr0, RefPicSetStCurr1, RefPicSetStFoll0 andRefPicSetStFoll1 are collectively referred to as the short-term subsetof the reference picture set. RefPicSetLtCurr and RefPicSetLtFoll arecollectively referred to as the long-term subset of the referencepicture set.

In HEVC, a reference picture set may be specified in a sequenceparameter set and taken into use in the slice header through an index tothe reference picture set. A reference picture set may also be specifiedin a slice header. A reference picture set may be coded independently ormay be predicted from another reference picture set (known as inter-RPSprediction). In both types of reference picture set coding, a flag(used_by_curr_pic_X_flag) is additionally sent for each referencepicture indicating whether the reference picture is used for referenceby the current picture (included in a *Curr list) or not (included in a*Foll list). Pictures that are included in the reference picture setused by the current slice are marked as “used for reference”, andpictures that are not in the reference picture set used by the currentslice are marked as “unused for reference”. If the current picture is anIDR picture, RefPicSetStCurr0, RefPicSetStCurr1, RefPicSetStFoll0,RefPicSetStFoll1, RefPicSetLtCurr, and RefPicSetLtFoll are all set toempty.

In many coding modes of H.264/AVC and HEVC, the reference picture forinter prediction is indicated with an index to a reference picture list.The index may be coded with variable length coding, which usually causesa smaller index to have a shorter value for the corresponding syntaxelement. In H.264/AVC and HEVC, two reference picture lists (referencepicture list 0 and reference picture list 1) are generated for eachbi-predictive (B) slice, and one reference picture list (referencepicture list 0) is formed for each inter-coded (P) slice.

A reference picture list, such as reference picture list 0 and referencepicture list 1, is typically constructed in two steps: First, an initialreference picture list is generated. The initial reference picture listmay be generated for example on the basis of POC, or information on theprediction hierarchy, or any combination thereof. Second, the initialreference picture list may be reordered by reference picture listreordering (RPLR) commands, also known as reference picture listmodification syntax structure, which may be contained in slice headers.If reference picture sets are used, the reference picture list 0 may beinitialized to contain RefPicSetStCurr0 first, followed byRefPicSetStCurr1, followed by RefPicSetLtCurr. Reference picture list 1may be initialized to contain RefPicSetStCurr1 first, followed byRefPicSetStCurr0. In HEVC, the initial reference picture lists may bemodified through the reference picture list modification syntaxstructure, where pictures in the initial reference picture lists may beidentified through an entry index to the list. In other words, in HEVC,reference picture list modification is encoded into a syntax structurecomprising a loop over each entry in the final reference picture list,where each loop entry is a fixed-length coded index to the initialreference picture list and indicates the picture in ascending positionorder in the final reference picture list.

Many coding standards, including H.264/AVC and HEVC, may have decodingprocess to derive a reference picture index to a reference picture list,which may be used to indicate which one of the multiple referencepictures is used for inter prediction for a particular block. Areference picture index may be coded by an encoder into the bitstream insome inter coding modes or it may be derived (by an encoder and adecoder) for example using neighboring blocks in some other inter codingmodes.

FIGS. 1 a and 1 b illustrate an example of a camera having multiplelenses and imaging sensors but also other types of cameras may be usedto capture wide view images and/or wide view video.

In the following, the terms wide view image and wide view video mean animage and a video, respectively, which comprise visual informationhaving a relatively large viewing angle, larger than 100 degrees. Hence,a so called 360 panorama image/video as well as images/videos capturedby using a fish eye lens may also be called as a wide view image/videoin this specification. More generally, the wide view image/video maymean an image/video in which some kind of projection distortion mayoccur when a direction of view changes between successive images orframes of the video so that a transform may be needed to find outco-located pixels from a reference image or a reference frame. This willbe described in more detail later in this specification.

The camera 100 of FIG. 1 a comprises two or more camera units 102 and iscapable of capturing wide view images and/or wide view video. In thisexample the number of camera units 102 is eight, but may also be lessthan eight or more than eight. Each camera unit 102 is located at adifferent location in the multi-camera system and may have a differentorientation with respect to other camera units 102. As an example, thecamera units 102 may have an omnidirectional constellation so that ithas a 360 viewing angle in a 3D-space. In other words, such camera 100may be able to see each direction of a scene so that each spot of thescene around the camera 100 can be viewed by at least one camera unit102.

The camera 100 of FIG. 1 a may also comprise a processor 104 forcontrolling the operations of the camera 100. There may also be a memory106 for storing data and computer code to be executed by the processor104, and a transceiver 108 for communicating with, for example, acommunication network and/or other devices in a wireless and/or wiredmanner. The camera 100 may further comprise a user interface (UI) 110for displaying information to the user, for generating audible signalsand/or for receiving user input. However, the camera 100 need notcomprise each feature mentioned above, or may comprise other features aswell. For example, there may be electric and/or mechanical elements foradjusting and/or controlling optics of the camera units 102 (not shown).

FIG. 1 a also illustrates some operational elements which may beimplemented, for example, as a computer code in the software of theprocessor, in a hardware, or both. A focus control element 114 mayperform operations related to adjustment of the optical system of cameraunit or units to obtain focus meeting target specifications or someother predetermined criteria. An optics adjustment element 116 mayperform movements of the optical system or one or more parts of itaccording to instructions provided by the focus control element 114. Itshould be noted here that the actual adjustment of the optical systemneed not be performed by the apparatus but it may be performed manually,wherein the focus control element 114 may provide information for theuser interface 110 to indicate a user of the device how to adjust theoptical system.

FIG. 1 b shows as a perspective view the camera 100 of FIG. 1 a . InFIG. 1 b seven camera units 102 a-102 g can be seen, but the camera 100may comprise even more camera units which are not visible from thisperspective. FIG. 1 b also shows two microphones 112 a, 112 b, but theapparatus may also comprise one or more than two microphones.

It should be noted here that embodiments disclosed in this specificationmay also be implemented with apparatuses having only one camera unit 102or less or more than eight camera units 102 a-102 g.

In accordance with an embodiment, the camera 100 may be controlled byanother device (not shown), wherein the camera 100 and the other devicemay communicate with each other and a user may use a user interface ofthe other device for entering commands, parameters, etc. and the usermay be provided information from the camera 100 via the user interfaceof the other device.

Terms 360-degree video or virtual reality (VR) video may be usedinterchangeably. They may generally refer to video content that providessuch a large field of view that only a part of the video is displayed ata single point of time in typical displaying arrangements. For example,a virtual reality video may be viewed on a head-mounted display (HMD)that may be capable of displaying e.g. about 100-degree field of view(FOV). The spatial subset of the virtual reality video content to bedisplayed may be selected based on the orientation of the head-mounteddisplay. In another example, a flat-panel viewing environment isassumed, wherein e.g. up to 40-degree field-of-view may be displayed.When displaying wide field of view content (e.g. fisheye) on such adisplay, it may be preferred to display a spatial subset rather than theentire picture.

MPEG omnidirectional media format (OMAF) may be described with FIGS. 2 aand 2 b.

360-degree image or video content may be acquired and prepared forexample as follows. Images or video can be captured by a set of camerasor a camera device with multiple lenses and imaging sensors. Theacquisition results in a set of digital image/video signals. Thecameras/lenses may cover all directions around the center point of thecamera set or camera device. The images of the same time instance arestitched, projected, and mapped onto a packed virtual reality frame,which may alternatively be referred to as a packed picture. The mappingmay alternatively be referred to as region-wise mapping or region-wisepacking. The breakdown of image stitching, projection, and mappingprocesses are illustrated with FIG. 2 a and described as follows. Inputimages 201 are stitched and projected 202 onto a three-dimensionalprojection structure, such as a sphere or a cube. The projectionstructure may be considered to comprise one or more surfaces, such asplane(s) or part(s) thereof. A projection structure may be defined as athree-dimensional structure consisting of one or more surface(s) onwhich the captured virtual reality image/video content may be projected,and from which a respective projected frame can be formed. The imagedata on the projection structure is further arranged onto atwo-dimensional projected frame 203. The term projection may be definedas a process by which a set of input images are projected onto aprojected frame or a projected picture. There may be a pre-defined setof representation formats of the projected frame, including for examplean equirectangular panorama and a cube map representation format.

Region-wise mapping 204 may be applied to map projected frames 203 ontoone or more packed virtual reality frames 205. In some cases, theregion-wise mapping may be understood to be equivalent to extracting twoor more regions from the projected frame, optionally applying ageometric transformation (such as rotating, mirroring, and/orresampling) to the regions, and placing the transformed regions inspatially non-overlapping areas, a.k.a. constituent frame partitions,within the packed virtual reality frame. If the region-wise mapping isnot applied, the packed virtual reality frame 205 may be identical tothe projected frame 203. Otherwise, regions of the projected frame aremapped onto a packed virtual reality frame by indicating the location,shape, and size of each region in the packed virtual reality frame. Theterm mapping may be defined as a process by which a projected frame ismapped to a packed virtual reality frame. The term packed virtualreality frame may be defined as a frame that results from a mapping of aprojected frame. In practice, the input images 201 may be converted topacked virtual reality frames 205 in one process without intermediatesteps.

Packing information may be encoded as metadata in or along thebitstream. For example, the packing information may comprise aregion-wise mapping from a pre-defined or indicated source format to thepacked frame format, e.g. from a projected frame to a packed VR frame,as described earlier. The region-wise mapping information may forexample comprise for each mapped region a source rectangle in theprojected frame and a destination rectangle in the packed VR frame,where samples within the source rectangle are mapped to the destinationrectangle and rectangles may for example be indicated by the locationsof the top-left corner and the bottom-right corner. The mapping maycomprise resampling. Additionally or alternatively, the packinginformation may comprise one or more of the following: the orientationof the three-dimensional projection structure relative to a coordinatesystem, indication which omnidirectional projection format is used,region-wise quality ranking indicating the picture quality rankingbetween regions and/or first and second spatial region sequences, one ormore transformation operations, such as rotation by 90, 180, or 270degrees, horizontal mirroring, and vertical mirroring. The semantics ofpacking information may be specified in a manner that they areindicative for each sample location within packed regions of a decodedpicture which is the respective spherical coordinate location.

In 360-degree systems, a coordinate system may be defined throughorthogonal coordinate axes, such as X (lateral), Y (vertical, pointingupwards), and Z (back-to-front axis, pointing outwards). Rotationsaround the axes may be defined and may be referred to as yaw, pitch, androll. Yaw may be defined to rotate around the Y axis, pitch around the Xaxis, and roll around the Z axis. Rotations may be defined to beextrinsic, i.e., around the X, Y, and Z fixed reference axes. The anglesmay be defined to increase clockwise when looking from the origintowards the positive end of an axis. The coordinate system specified canbe used for defining the sphere coordinates, which may be referred toazimuth (ϕ) and elevation (θ).

Global coordinate axes may be defined as coordinate axes, e.g. accordingto the coordinate system as discussed above, that are associated withaudio, video, and images representing the same acquisition position andintended to be rendered together. The origin of the global coordinateaxes is usually the same as the center point of a device or rig used foromnidirectional audio/video acquisition as well as the position of theobserver's head in the three-dimensional space in which the audio andvideo tracks are located. In the absence of the initial viewpointmetadata, the playback may be recommended to be started using theorientation (0, 0) in (azimuth, elevation) relative to the globalcoordinate axes.

As mentioned above, the projection structure may be rotated relative tothe global coordinate axes. The rotation may be performed for example toachieve better compression performance based on the spatial and temporalactivity of the content at certain spherical parts. Alternatively oradditionally, the rotation may be performed to adjust the renderingorientation for already encoded content. For example, if the horizon ofthe encoded content is not horizontal, it may be adjusted afterwards byindicating that the projection structure is rotated relative to theglobal coordinate axes. The projection orientation may be indicated asyaw, pitch, and roll angles that define the orientation of theprojection structure relative to the global coordinate axes. Theprojection orientation may be included e.g. in a box in a sample entryof an ISOBMFF track for omnidirectional video.

360-degree panoramic content (i.e., images and video) cover horizontallythe full 360-degree field-of-view around the capturing position of animaging device. The vertical field-of-view may vary and can be e.g. 180degrees. Panoramic image covering 360-degree field-of-view horizontallyand 180-degree field-of-view vertically can be represented by a spherethat has been mapped to a two-dimensional image plane usingequirectangular projection (ERP). In this case, the horizontalcoordinate may be considered equivalent to a longitude, and the verticalcoordinate may be considered equivalent to a latitude, with notransformation or scaling applied. In some cases panoramic content with360-degree horizontal field-of-view but with less than 180-degreevertical field-of-view may be considered special cases ofequirectangular projection, where the polar areas of the sphere have notbeen mapped onto the two-dimensional image plane. In some casespanoramic content may have less than 360-degree horizontal field-of-viewand up to 180-degree vertical field-of-view, while otherwise have thecharacteristics of equirectangular projection format.

In cube map projection format, spherical video is projected onto the sixfaces (a.k.a. sides) of a cube. The cube map may be generated e.g. byfirst rendering the spherical scene six times from a viewpoint, with theviews defined by an 90 degree view frustum representing each cube face.The cube sides may be frame-packed into the same frame or each cube sidemay be treated individually (e.g. in encoding). There are many possibleorders of locating cube sides onto a frame and/or cube sides may berotated or mirrored. The frame width and height for frame-packing may beselected to fit the cube sides “tightly” e.g. at 3×2 cube side grid, ormay include unused constituent frames e.g. at 4×3 cube side grid.

A cube map can be stereoscopic. A stereoscopic cube map can e.g. bereached by re-projecting each view of a stereoscopic panorama to thecube map format.

The process of forming a monoscopic equirectangular panorama picture isillustrated in FIG. 2 b , in accordance with an embodiment. A set ofinput images 211, such as fisheye images of a camera array or a cameradevice 100 with multiple lenses and sensors 102, is stitched 212 onto aspherical image 213. The spherical image 213 is further projected 214onto a cylinder 215 (without the top and bottom faces). The cylinder 215is unfolded 216 to form a two-dimensional projected frame 217. Inpractice one or more of the presented steps may be merged; for example,the input images 213 may be directly projected onto a cylinder 217without an intermediate projection onto the sphere 213 and/or to thecylinder 215. The projection structure for equirectangular panorama maybe considered to be a cylinder that comprises a single surface.

The equirectangular projection may be defined as a process that convertsany sample location within the projected picture (of the equirectangularprojection format) to sphere coordinates of a coordinate system. Thesample location within the projected picture may be defined relative topictureWidth and pictureHeight, which are the width and height,respectively, of the equirectangular panorama picture in samples. In thefollowing, let the center point of a sample location along horizontaland vertical axes be denoted as i and j, respectively. The spherecoordinates (ϕ, θ) for the sample location, in degrees, are given by thefollowing equirectangular mapping equations: ϕ=(0.5−i÷pictureWidth)*360,0=(0.5−j÷pictureHeight)*180. It is noted that depending on the directionof axes for (ϕ, θ) different conversion formulas may be derived.

In general, 360-degree content can be mapped onto different types ofsolid geometrical structures, such as polyhedron (i.e. athree-dimensional solid object containing flat polygonal faces, straightedges and sharp corners or vertices, e.g., a cube or a pyramid),cylinder (by projecting a spherical image onto the cylinder, asdescribed above with the equirectangular projection), cylinder (directlywithout projecting onto a sphere first), cone, etc. and then unwrappedto a two-dimensional image plane. The two-dimensional image plane canalso be regarded as a geometrical structure. In other words, 360-degreecontent can be mapped onto a first geometrical structure and furtherunfolded to a second geometrical structure. However, it may be possibleto directly obtain the transformation to the second geometricalstructure from the original 360-degree content or from other wide viewvisual content. In general, an omnidirectional projection format may bedefined as a format to represent (up to) 360-degree content on atwo-dimensional image plane. Examples of omnidirectional projectionformats include the equirectangular projection format and the cubemapprojection format.

In some cases panoramic content with 360-degree horizontal field-of-viewbut with less than 180-degree vertical field-of-view may be consideredspecial cases of equirectangular projection, where the polar areas ofthe sphere have not been mapped onto the two-dimensional image plane. Insome cases a panoramic image may have less than 360-degree horizontalfield-of-view and up to 180-degree vertical field-of-view, whileotherwise has the characteristics of equirectangular projection format.

Human eyes are not capable of viewing the whole 360 degrees space, butare limited to a maximum horizontal and vertical field-of-views (HHFoV,HVFoV). Also, a HMD device has technical limitations that allow onlyviewing a subset of the whole 360 degrees space in horizontal andvertical directions (DHFoV, DVFoV)).

In many displaying situations only a partial picture is needed to bedisplayed while the remaining picture is required to be decoded but isnot displayed. These displaying situations include:

-   -   Typical head-mounted displays (HMDs) display ˜100 degrees field        of view, while often the input video for HMD consumption covers        entire 360 degrees.    -   Typical flat-panel viewing environments display up to 40-degree        field-of-view. When displaying wide-FOV content (e.g. fisheye)        on such a display, it may be preferred to display a spatial        subset rather than the entire picture.

A viewport may be defined as a region of omnidirectional image or videosuitable for display and viewing by the user. A current viewport (whichmay be sometimes referred simply as a viewport) may be defined as thepart of the spherical video that is currently displayed and hence isviewable by the user(s). At any point of time, a video rendered by anapplication on a HMD renders a portion of the 360-degrees video, whichis referred to as a viewport. Likewise, when viewing a spatial part ofthe 360-degree content on a conventional display, the spatial part thatis currently displayed is a viewport. A viewport is a window on the360-degrees world represented in the omnidirectional video displayed viaa rendering display. A viewport may be characterized by a horizontalfield-of-view (VHFoV) and a vertical field-of-view (VVFoV). In thefollowing, the horizontal field-of-view of the viewport will beabbreviated with HFoV and, respectively, the vertical field-of-view ofthe viewport will be abbreviated with VFoV. As used herein the termomnidirectional video or image content may refer to content that hasgreater spatial extent than the field-of-view of the device renderingthe content. Omnidirectional content may cover substantially 360 degreesin horizontal dimension and substantially 180 degrees in verticaldimension, but “omnidirectional” may also refer to content covering lessthan the entire 360 degree view in horizontal direction and/or the 180degree view in vertical direction.

A sphere region may be defined as a region on a sphere that may bespecified by four great circles or by two azimuth circles and twoelevation circles and additionally by a tile angle indicating rotationalong the axis originating from the sphere origin passing through thecentre point of the sphere region. A great circle may be defined as anintersection of the sphere and a plane that passes through the centrepoint of the sphere. A great circle is also known as an orthodrome orRiemannian circle. An azimuth circle may be defined as a circle on thesphere connecting all points with the same azimuth value. An elevationcircle may be defined as a circle on the sphere connecting all pointswith the same elevation value.

OMAF specifies a generic timed metadata syntax for sphere regions. Apurpose for the timed metadata track is indicated by the track sampleentry type. The sample format of all metadata tracks for sphere regionsspecified starts with a common part and may be followed by an extensionpart that is specific to the sample entry of the metadata track. Eachsample specifies a sphere region.

One of the specific sphere region timed metadata tracks specified inOMAF is known as recommended viewport timed metadata track, whichindicates the viewport that should be displayed when the user does nothave control of the viewing orientation or has released control of theviewing orientation. The recommended viewport timed metadata track maybe used for indicating a recommended viewport based on a director's cutor based on measurements of viewing statistics. A textual description ofthe recommended viewport may be provided in the sample entry. The typeof the recommended viewport may be indicated in the sample entry and maybe among the following:

-   -   A recommended viewport per the director's cut, i.e., a viewport        suggested according to the creative intent of the content author        or content provider.    -   A recommended viewport selected based on measurements of viewing        statistics.    -   Unspecified (for use by applications or specifications other        than OMAF).

Videos and/or images may be overlaid on an omnidirectional video and/orimage. The coded overlaying video can be a separate stream or part ofthe bitstream of the currently rendered 360-degree video/image. However,the overlaying process may be based on certain conditions.

The omnidirectional streaming system may overlay a video/image on top ofthe omnidirectional video/image being rendered. The overlaying processmay cover the overlaid video/image or a part of the video/image or theremay be some level of transparency or more than one levels oftransparency wherein the overlaid video/image may be seen under theoverlaying video/image but with less brightness. In other words, therecould be an associated level of transparency corresponding to thevideo/image in foreground (overlay) and the video/image in background(video/image of VR scene).

In accordance with an embodiment, the overlaid region may have one ormore than one levels of transparency. For example, the overlaid regionmay have different parts with different levels of transparency. Inaccordance with an embodiment, the transparency level could be definedto be within a certain range, such as from 0 to 1 so that the smallerthe value the smaller is the transparency, or vice versa. In the exampleof FIG. 6 d , the area in which the watch and time text are shown, couldhave a first level of transparency, e.g. 0 (not transparent), and theremaining parts of the overlay area could have a second level oftransparency different from the first level, for example 0.5.

Additionally, the content provider may choose to overlay a part of thesame omnidirectional video over the current viewport of the user. Thecontent provider may want to overlay the video based on the viewingcondition of the user. For example, overlaying may be performed, if theuser's viewport does not match the content provider's recommendedviewport. In this case, the client player logic overlays the contentproviders recommended viewport (as a preview window) on top of thecurrent viewport of the user. It may also be possible to overlay therecommended viewport, if the user's current viewport does not match,such that the position of the overlaid video is based on the directionin which the user is viewing. For example, overlaying the recommendedviewport to the left of the display, if the recommended viewport is tothe left of the user's current viewport. It may also be possible tooverlay the whole 360-degree video. Yet another example is to use theoverlaying visual information as a guidance mechanism to guide the usertowards the recommended viewport, for example guiding people who arehearing impaired.

Thus, there is a need for signaling of overlaying of videos/imagesand/or timed text along with the location of the overlay together withthe conditions on overlaying in the above case.

The OMAF standard supports region-wise frame packing, however there isno signaling mechanism for overlaying and signaling of conditions underwhich the overlaying is to be done. HEVC provides the possibility toinclude overlay video sequences into the bitstream as auxiliary picturelayers. The overlay information SEI message provides information aboutoverlay pictures coded as auxiliary pictures. Each overlay auxiliarypicture layer is associated with one or more primary picture layers. Theoverlay support in HEVC can be controlled only as a function of time(i.e., the content author can determine and signal the time periodduring which an overlay picture or video is displayed) but is otherwiseunconditional.

In the following, some examples of signaling will be described in moredetail.

The FIG. 6 a illustrates an example of an omnidirectional video/imagefrom an event, for example a dance party. The video/image frame 61 isrepresented by the equirectangular projection, althoughproblems/solutions described herein apply more generally to all theprojection formats used for representing omnidirectional videos/images.

Furthermore, the omnidirectional video/image may have a region called adirector's viewport also known as a recommended viewport 63, whichrepresents a spatial area in the video/image frame which can, forexample, represent one of the following. The director's viewport may beprescribed by the content provider/author. It may represent the regionwhich was viewed by the user's friend or the region which was selectedbased on measurements of viewing statistics by a crowd. However, thedirector's viewport is not limited to these examples but may representsome other visual information.

The term current viewport refers to the region that is currently beingdisplayed to the user. An example of this kind of region is illustratedin FIG. 6 a as the dotted area 62. This dotted area represents thecurrent viewport 65 shown in FIG. 6 b . In many viewing modes, the userconsuming the video/image may choose the current viewport freely. Forexample, when viewing happens with a head-mounted display, theorientation of the head determines the viewing orientation and hence theviewport. Thus, the user views a spatial region/area, which may be thesame as or may differ from the director's viewport.

In the following, some examples of the term visual overlay will bedescribed. The visual overlay may be an overlay video sequence (a.k.a.an overlaying video sequence), an overlay image (a.k.a. an overlayingimage), an overlay text (a.k.a. an overlaying text), which may be staticor dynamic/timed, overlay graphics (a.k.a. overlaying graphics), whichmay also be static or dynamic/timed. The visual overlay may also be acombination of two or more of the above-mentioned alternatives. As anon-limiting example, the visual overlay may comprise an overlay videosequence and an overlay text. An example of overlay text and image isdepicted in FIG. 6 d.

It needs to be understood that even though some embodiments aredescribed with reference to an overlay video sequence and/or an overlayimage, they equally apply to any type of a visual overlay.

In FIG. 6 b the director's viewport is overlaying the current viewport65 in the region 64 on the left side of the current viewport.

There may be one or more conditions on when and how to display thevisual overlay. Therefore, a rendering device may need to receiveinformation which the rendering device may use to perform the overlayingas indicated by the signaled information.

In the following, some steps of delivering omnidirectional content andoverlaying content and signaling will be described with reference to theflow diagram of FIG. 10 a . A content author obtains 71 theomnidirectional content and the overlaying content and provides them toan encapsulating device, which may be, for example, a part of an encoderor another apparatus. The omnidirectional content may be encapsulated 72and stored in, for example, a container file, and may be described in amanifest. The content author generates 73 a first indication and insertsthe first indication in a bitstream, in a container file, and/or in amanifest. The first indication indicates the omnidirectional videosequence or image to be delivered to a content rendering device. Thecontent author may also generate 74 a second indicator indicating thevisual overlay, intended to be overlaid, under certain conditions, onthe omnidirectional video sequence or image for displaying. The secondindicator may also be inserted in a bitstream, a container file, and/ora manifest. Furthermore, the content author may determine 75 overlayingconditions such as how, where and when the omnidirectional videosequence or image or part of it is intended to be overlaid by theoverlaying content. The overlaying conditions may include a firstcondition in which case the visual overlay is to be overlaid or a secondcondition in which case the visual overlay is not to be overlaid. Then,the content author may also generate 76 a third indication indicatingthe first condition or the second condition. The third indication mayalso be inserted in a bitstream, a container file, and/or a manifest.

The omnidirectional content, the overlaying content and the indicatorsmay be stored into one or more files and/or delivered to a receivingapparatus, for example when a request for content delivery is receivedfrom the receiving apparatus.

The receiving apparatus may perform the following operations, alsoillustrated as a flow diagram in FIG. 10 b , to render the receivedcontents. The receiving apparatus may receive 90 a bitstream, acontainer file, and/or a manifest, and parse 91, from the bitstream, acontainer file, and/or a manifest, the first indication of theomnidirectional video sequence or image. The receiving apparatus mayalso parse 92, from the bitstream, the container file, and/or themanifest, the second indication of a visual overlay, intended to beoverlaid, under certain conditions, on the omnidirectional videosequence or image for displaying. Furthermore, the receiving apparatusmay parse 93, from the bitstream, the container file, and/or themanifest, the first condition in which case the visual overlay is to beoverlaid or the second condition in which case the visual overlay is notto be overlaid. The receiving apparatus may decode the omnidirectionalvideo sequence or image. The receiving apparatus may then render 94 thedecoded omnidirectional video sequence or image and show it on a displayof the receiving apparatus or deliver the omnidirectional video sequenceor image to another apparatus capable for displaying the omnidirectionalvideo sequence or image. The receiving apparatus may also examine 95whether the first condition or the second condition was received. If thefirst condition was received, the receiving apparatus may examine 96whether the first condition is fulfilled or not. The receiving apparatusmay decode the overlaying content. If the examination reveals that thefirst condition is fulfilled, the receiving apparatus may render 97 thedecoded overlaying content on the display or deliver the overlayingcontent to the other apparatus which may display the overlaying content.If, however, the second condition was received, the receiving apparatusmay examine 98 whether the second condition is fulfilled or not. If theexamination reveals that the second condition is fulfilled, theoverlaying content will not be shown. On the other hand, if theexamination reveals that the second condition is not fulfilled, thereceiving apparatus may render 97 the overlaying content on the displayor deliver the overlaying content to the other apparatus which maydisplay the overlaying content.

Although it was described above that the receiving apparatus performsthe examining of the first/second condition, it may be possible that thereceiving apparatus sends information of the first/second condition andthe overlaying content to the optional other apparatus, which may thenperform the examination of the first/second condition and determinewhether to show the overlaying content or not.

FIG. 9 a shows some elements of a video encoding section 510, inaccordance with an embodiment. The video encoding section 510 may be apart of the omnidirectional streaming system 600 or separate from it. Asignaling constructor 512 may comprise a first input 511 a to obtainomnidirectional video/image, a second input 511 b to obtain visualoverlay, and a third input 511 a to obtain overlay conditions 511 c. Thesignaling constructor 512 forms different kinds of signals and providesthem to an encoding element 513. The encoding element 513 may encode thesignals as well as the omnidirectional video/image and the visualoverlay for storing and/or transmission. However, there may be separateencoding elements for signal encoding and visual information encoding.

FIG. 9 b shows a video decoding section 520, in accordance with anembodiment. Also the video encoding section 510 may be a part of theomnidirectional streaming system 600 or separate from it. The videodecoding section 520 may obtain signaling data via a first input 521 andencoded visual information (omnidirectional video/image, visual overlay)via a second input 522. The signaling data and the encoded visualinformation may be decoded by a decoding element 523. Decoded signalingdata may be used by a rendering element 524 to control in imagereconstruction from decoded visual information. The rendering element524 may also receive viewport data 525 to determine the location of acurrent viewport within the image area of the omnidirectionalvideo/image).

In the following some examples of utilization of the visual overlayswill be described. One use case for visual overlays is to display therecommended viewport. The recommended viewport displayed as a visualoverlay may, for example, be a selectable item. When the user selectsthe recommended viewport, the viewing orientation may be changed to thatorientation. Additionally, one option applicable particularly for 2Dviewing on a conventional display, such as on a laptop screen, is thatby selecting the recommended viewport overlay, the user releases controlof the viewing orientation, after which the current viewport follows therecommended viewport. An example of overlaying the director's viewporton the user's current viewport is illustrated in FIG. 6 b.

FIG. 6 c illustrates another example of overlaying the whole 360-degreevideo on the user's current viewport.

As was motivated above, the conditions for overlaying may include butare not restricted to: the user's current viewport does not overlap withthe region representing the director's viewport. The related embodimentsmay be described as follows:

In an embodiment, a content authoring method such as for example thatdescribed with FIG. 10 a further comprises indicating, in the bitstream,the container file, and/or the manifest, that visual overlay representsa recommended viewport.

In an embodiment, the content authoring method further comprisesconcluding, based on indicating visual overlay representing arecommended viewport, the second condition that the visual overlayrepresenting the recommended viewport is not to be overlaid on theomnidirectional video sequence or image in a case that a currentviewport covers the visual overlay. In some embodiments, the secondcondition may indicate and/or the method or an apparatus may determinenot to render the overlay content when the current viewport at leastpartially covers the recommended viewport. In an alternative embodiment,the content authoring method further comprises indicating, in thebitstream, the container file, and/or in the manifest, the secondcondition that the visual overlay representing the recommended viewportis not to be overlaid on the omnidirectional video sequence or image ina case that a current viewport covers the visual overlay.

In an embodiment, a content consumption method such as that describedwith FIG. 10 b further comprises parsing, from the bitstream, thecontainer file, and/or the manifest, that visual overlay represents arecommended viewport.

In an embodiment, the content consumption method further comprisesconcluding, based on parsing that the visual overlay represents arecommended viewport, the second condition that the visual overlayrepresenting the recommended viewport is not to be overlaid on theomnidirectional video sequence or image in a case that a currentviewport covers the visual overlay. In an alternative embodiment, thecontent consumption method further comprises parsing, from thebitstream, the container file, and/or the manifest, the second conditionthat the visual overlay representing the recommended viewport is not tobe overlaid on the omnidirectional video sequence or image in a casethat a current viewport covers the visual overlay.

Several embodiments relate to indicating in a bitstream, a containerfile, and/or a manifest or parsing information from a bitstream, acontainer file, and/or a manifest. The bitstream may, for example, be avideo or image bitstream (such as an HEVC bitstream), wherein theindicating may utilize, for example, supplemental enhancementinformation (SEI) messages. The container file may, for example, complywith the ISO base media file format, the Matroska file format, or theMaterial eXchange Format (MXF). The manifest may, for example, conformto the Media Presentation Description (MPD) of MPEG-DASH (ISO/IEC23009-1), the M3U format, or the Composition Playlist (CPL) of theInteroperable Master Format (IMF). It needs to be understood that theseformats are provided as examples and that embodiments are not limited tothem. Embodiments may be similarly realized with any other similarcontainer or media description formats, such as the Session DescriptionProtocol (SDP). Embodiments may be realized with a suite of bitstreamformat(s), container file format(s) and manifest format(s), in which theindications may be. MPEG OMAF is an example of such a suite of formats.

It needs to be understood that instead of or in addition to a manifest,embodiments similarly apply to a container file format and/or a mediabitstream. For example, instead of or in addition to indicating aspatial region to be overlaid and a spatial region for overlaying in amanifest, they can be indicated within metadata of a container fileformat that also contains or refers to the encoded bitstream.

In the following, some non-limiting examples of conditions foroverlaying will be described.

In an embodiment, the second condition is that the visual overlayrepresenting the recommended viewport is not to be overlaid on theomnidirectional video sequence or image in a case that a currentviewport fully or partly covers the visual overlay.

In an embodiment, the first condition is that the visual overlayrepresenting the recommended viewport is to be overlaid on theomnidirectional video sequence or image in a case that a currentviewport does not cover the visual overlay entirely.

In an embodiment, a condition indicates a device type. The condition mayfor example indicate that overlaying is not done when theomnidirectional video or image is played back on a device of aparticular type, such as for example a desktop computer where thefield-of-view is narrow, for example less than 60 degrees. The thresholdfield of view (FOV) or alternatively the horizontal threshold field ofview and/or the vertical threshold field of view may be indicated and/orparsed with the condition.

In an embodiment, several recommended viewport video sequences or imagesare indicated, in the bitstream, in the container file, and/or in themanifest, and/or parsed, from the bitstream, from the container file,and/or from the manifest, to be alternatives. Alternatively, severalrecommended viewport video sequences or images are pre-defined orconcluded to be alternatives.

In an embodiment, a condition is indicated or parsed to select a visualoverlay based on the viewport width and/or height. For example, two ormore pairs of a visual overlay (among alternatives) and a suitable rangeof viewport width and/or height may be indicated. When the width andheight of the viewport is within an indicated range, the correspondingvisual overlay is selected to be displayed. This mechanism may be usedfor example to keep the size of the visual overlay suitable so that itdoes not occupy too large an area on the viewport.

The rendering device may need to obtain some information for therendering the visual overlays. Such information may be delivered in abitstream, a container file, and/or a manifest, wherein the renderingdevice may parse from the bitstream, the container file, and/or themanifest, one or more of the following pieces of information.

The information may comprise an indication of the location of a visualoverlay. This may be indicated, for example, relative to the viewportand may, for example, be indicated with and/or parsed as one of thefollowing: a two-dimensional location on a reference viewport or arelative 2D location from a reference point of the viewport.

When the indication is the two-dimensional location on a referenceviewport, the reference viewport may have pre-defined or indicated widthand height in pixels. The 2D location, such as the pixel coordinates onthe reference viewport for the top-left coordinate of the visual overlaymay be indicated. The reference viewport may be scaled to the actualviewport used in the viewing device, using a pre-defined or indicatedscaling method. For example, the width and height may be scaledseparately. In another example, the scaling maintains the picture aspectratio of the reference viewport and the scaled reference viewport iscentralized on the actual viewport.

When the indication is the relative 2D location from a reference pointof the viewport, a set of potential reference points may be pre-definedor signaled and may, for example, comprise the top-left corner, thetop-right corner, the bottom-left corner, the bottom-right corner andthe center point. The reference point may be pre-defined or signaled,e.g. by referencing to the set of potential reference points. Areference point of the visual overlay may be pre-defined, concluded fromthe reference point of the viewport, or signaled. For example, if thetop-left corner of the viewport is the reference point of the viewport,the top-left corner of the visual overlay may be concluded to be thereference point of the visual overlay. The relative 2D location may befor example given as percentages of the width and height of theviewport.

The location of a visual overlay may be indicated relative to theomnidirectional video or image and may, for example, be indicated withand/or parsed as one of the following: a 2D location on a projectedpicture, such as the pixel coordinates on the projected picture for thetop-left coordinate of the visual overlay, or as sphere coordinates suchas azimuth (ϕ) and elevation (θ) that identify a location of a referencepoint on the unit sphere, where the reference point may for example bethe center point of the visual overlay.

The indication may indicate that a recommended viewport video sequenceor image is the overlay video sequence or image. The recommendedviewport video sequence may be indicated using a recommended viewporttimed metadata track, for example as specified in MPEG OMAF, where thesphere coordinates (of the center point of the viewport), the tiltangle, and the viewport extents are provided and may be dynamicallychanging.

The indication may indicate that the visual overlay is a region on apacked picture of the omnidirectional video or image. The location ofthe region on the projected picture may be provided similarly to thelocation of packed regions on the projected picture in MPEG OMAF.

The indication may indicate that the visual overlay is a specific tileset of the omnidirectional video or image, where the tile set may becoded as a motion-constrained tile set.

The indication may indicate that the visual overlay is a separatestream, such as a separate MPEG-DASH Representation, from theomnidirectional video or image.

The indication may comprise an indication of the area the visual overlayis laid over, i.e. the spatial region on which the overlaying is done.This may comprise a location indicated as described above for the visualoverlay. This may also comprise a size, which may be indicated forexample as a width and height in pixels on the viewport or as horizontaland vertical field of view (or equivalently azimuth and elevation range)on a sphere. If the visual overlay has a different size than what isindicated for the area, the visual overlay may be scaled to the size ofthe area.

The indication may comprise an indication of an aspect ratio withrespect to the display field of view.

The indication may also comprise at least one value indicative of atransparency of the overlaid video.

In the following, adapting the visual appearance of the overlayconditionally will be described, in accordance with an embodiment.

The visual appearance of the visual overlay may be conditioned. Thecondition(s) are signaled by a content author and parsed by a renderingdevice (a.k.a. a player or a client apparatus). For a visual overlayrepresenting a recommended viewport, the condition(s) may include butare not limited to the following:

The condition may indicate that the location of the visual overlay isselected to indicate the direction of the recommended viewport relativeto the current viewport. For example, if the recommended viewport has agreater elevation angle than the current viewport, the visual overlaymay be located at top side of the viewport.

The condition may indicate that the rotation of the visual overlay isselected to indicate the tilt angle difference between the recommendedviewport and the current viewport.

This may be useful e.g. in 2D viewing.

The condition may indicate that the width and height of the visualoverlay is selected so that it indicates the closeness of therecommended viewport relative to the current viewport. For example, thevisual overlay may increase in size when the current viewport getscloser to the recommended viewport.

The condition may indicate that the transparency level of the visualoverlay is selected so that it indicates the closeness of therecommended viewport relative to the current viewport. For example, thevisual overlay may become more transparent when the current viewportgets closer to the recommended viewport.

Some related embodiments may be described for example as follows:

In an embodiment, the content authoring method further comprisesindicating, in the bitstream, in the container file, and/or in themanifest, an intended displaying effect for the visual overlayrepresenting a recommended viewport, and indicating, in the bitstream,in the container file, and/or in the manifest, at least one parameterfor controlling the displaying effect.

In an embodiment, the content consumption method further comprisesparsing, from the bitstream, from the container file, and/or from themanifest, an intended displaying effect for the visual overlayrepresenting a recommended viewport, and parsing, from the bitstream,from the container file, and/or from the manifest, at least oneparameter for controlling the displaying effect.

In an embodiment, the at least one parameter comprises one or more ofthe following:

-   -   indication if and/or how a location of the visual overlay        representing the recommended viewport within the current        viewport depends on sphere coordinates of the current viewport        and sphere coordinates of the recommended viewport;    -   indication if and/or how rotation of the visual overlay        representing the recommended viewport within the current        viewport depends on tilt angle of the current viewport and tilt        angle of the recommended viewport;    -   indication if and/or how the visual overlay is scaled in width        and/or height according to a distance of the visual overlay        representing the recommended viewport from the current viewport        on a sphere;    -   indication if and/or how the transparency of visual overlay is        scaled in width and/or height according to a distance of the        visual overlay representing the recommended viewport from the        current viewport on a sphere;

In accordance with an embodiment, an apparatus is configured todetermine a spatial region to be overlaid and a spatial region foroverlaying within an encoded bitstream, and to include in a manifest thespatial region to be overlaid and the spatial region for overlaying ofan encoded bitstream.

In accordance with an embodiment, a client apparatus is configured toparse from a manifest a spatial region to be overlaid and a spatialregion for overlaying; to parse from the manifest at least one conditionindicative of the reason for overlaying; and to determine that thespatial region to be overlaid is suitable for displaying.

It needs to be understood that while many embodiments are describedusing singular forms of nouns, e.g. an encoded bitstream, a viewport, aspatial region, and so on, the embodiments generally apply to pluralforms of nouns.

The above described embodiments may help in enhancing the viewingexperience of the user. Furthermore, they may help the content author inguiding the viewer to his (authors) intended viewing conditions in theomnidirectional video/image.

In general, indications, conditions, and/or parameters described indifferent embodiments may be represented with syntax elements in syntaxstructure(s), such as SEI messages, in a video bitstream, and/or instatic or dynamic syntax structures in a container file, and/or in amanifest. An example of a static syntax structure in ISOBMFF is a box ina sample entry of a track. Another example of a static syntax structurein ISOBMFF is an item property for an image item. Examples of dynamicsyntax structures in ISOBMFF were described earlier with reference totimed metadata.

In the following, some example embodiments of the signaling are providedin more detailed manner.

TrackHeaderBox of ISOBMFF includes the layer syntax element. layerspecifies the front-to-back ordering of video tracks; tracks with lowernumbers are closer to the viewer. When overlaying video appears in onetrack and overlaid video in another track, the layer syntax element ofthe overlaid video track may be greater than that of the overlay videotrack. When there are several overlay video tracks, the layer valuesindicates their respective overlaying order.

Visual rendering guidance codepoint (VisualRenderingGuidance) may bespecified as unsigned integer, with certain semantics for each value.

Type: Unsigned integer, enumeration

Range: 0 to 255, inclusive

VisualRenderingGuidance indicates the intended processing for renderingthe associated visual track. The following values may be specified andother values may be reserved:

TABLE 1 Value Semantics 0 Non-head-tracked. The location of the decodedtrack stays at the same position on the display (i.e. the currentviewport) regardless of the user's viewing direction (i.e. headorientation when using a head-mounted display). 1 Head-tracked. Thedecoded track is regarded as a view surface that is displayed inhead-tracked fashion when user's viewing direction overlaps the viewsurface.

Visual Rendering Guidance Box

Definition

When the rendering of a visual track with respect to head orientation isconstant regardless of which other tracks it is presented with, thevisual rendering guidance may be included as VisualRenderingGuidanceBoxin each VisualSampleEntry of the track, and theVisualRenderingGuidanceBox indicates the processing that should beapplied when playing the decoded track.

VisualRenderingGuidanceBox indicates the processing that should beapplied to the decoded track (e.g. representing an overlay videosequence) when playing the associated tracks (e.g. representing theoverlaid omnidirectional video sequence).

Syntax. Visual rendering guidance information may include one or more ofthe following parameters:

aligned(8) class VisualRenderingGuidanceBox extends FullBox(‘virg’, 0,0) { unsigned int(8) rendering_guidance; unsigned int(8) stereo_idc; if(stereo_idc == 1) float(32) relative_disparity; if (rendering_guidance== 0) { // non-head-tracked unsigned int(8) loc_ref_pnt; float(32)rel_loc_x; float(32) rel_loc_y; } }

Semantics. Examples of the meaning of particular values of theparameters are provided below, but it is appreciated that any suitablevalues may be alternatively used.

rendering_guidance is an enumerated value VisualRenderingGuidance asspecified above.

stereo_idc equal to 0 specifies that the track contains one or both ofviews stereoscopic content or that monoscopic content is intended to bedisplayed without disparity (on screen level) when using a stereoscopicdisplay. stereo_idc equal to 1 specifies that monoscopic content isintended to be displayed on a particular depth level (as specified byrelative_disparity).

relative_disparity specifies the intended depth level on whichmonoscopic content should be displayed. relative_disparity is indicatedin units of relative screen widths on a rectilinear display having ahorizontal field of view of 90 degrees (i.e., a relative_disparity equalto 1 indicates a disparity of a screen width on a rectilinear displayhaving a horizontal field of view of 90 degrees). Negative valuescorrespond to depth levels in front of the screen level, 0 correspondsto the screen level, and positive values correspond to depth levelsbehind the screen level.

loc_ref_pnt specifies the reference point in the decoded content forwhich the relative location is provided. loc_ref_pnt equal to 0specifies the center point, and loc_ref_pnt equal to 1, 2, 3, and 4specifies top-left, top-right, bottom-left, and bottom-right corners ofthe decoded content, respectively.

rel_loc_x specifies the relative horizontal coordinate of the referencepoint in the range of −1 to 1, inclusive, where 0 is on the referencepoint, −1 is to the left from the reference point by the amount ofviewport width, and 1 is to the right from the reference point by theamount of viewport width. rel_loc_y specifies the relative verticalcoordinate of the reference point in the range of −1 to 1, inclusive,where 0 is on the reference point, −1 is above the reference point bythe amount of viewport height, and 1 is below the reference point by theamount of viewport height.

In another example, a timed metadata track is associated with a videotrack representing a 2D rectilinear overlay intended to appear on asignalled location within the current viewport. The timed metadata trackmay contain samples that indicate the location of the video track withinthe viewport. The location may be indicated for example withloc_ref_pnt, rel_loc_x, and rel_loc_y, or like described in any otherembodiment.

In yet another example, an overlay location timed metadata track such asdescribed in the previous paragraph is associated with a recommendedviewport timed metadata track. The association may be indicated in acontainer file for example as a track reference of a particular typebetween the tracks, or as such a track group of a particular type thatincludes both the tracks. A player should handle the indicatedassociation by concluding that the recommended viewport is an overlayvideo whose position within the current viewport is indicated in theoverlay location timed metadata track.

In the following, an example of overlay-based signaling will bedescribed.

In an embodiment, it is indicated in a manifest or parsed from amanifest whether the spatial region to be overlaid is monoscopic, leftor right view of stereoscopic content, or contains both of views ofstereoscopic content. The indication included in a manifest or parsedfrom a manifest may, for example, use one or more of the followingsemantics or alike:

Type: unsigned integer, enumeration

Range: 0-15

TABLE 2 Value Semantics 0 Monoscopic 1 Left view of stereoscopic content2 Right view of stereoscopic content 3 Both views of stereoscopiccontent 4-14 Reserved 15  Other/unknown

In an embodiment, the spatial region to be overlaid is indicated in amanifest or parsed from a manifest with reference to sphericalcoordinates indicating the position and, in some embodiments, theorientation, of the viewport on a sphere.

In an embodiment, the position of the spatial region on a sphere to beoverlaid is indicated using two angles of a spherical coordinate systemindicating a specific point of the viewport, such as the center point ora particular corner point of the viewport. The specific point may bepre-defined, e.g. in a manifest format specification, or may beindicated in a manifest and/or parsed from a manifest. For example, Yawand Pitch angles may be used, where Yaw indicates the Euler angle of thecenter point of the viewport, e.g. in degrees, relative to the referenceorientation, and Pitch indicates the Euler angle of the center point ofthe spatial region to be overlaid, e.g. in degrees, applied in the orderYaw followed by Pitch, relative to the reference orientation. Yaw isapplied prior to Pitch. Yaw rotates around the one coordinate axis (e.g.Y-axis), Pitch around another axis (e.g. the X-axis). The angles may bedefined to increase clockwise when looking away from the origin. Yaw maybe defined to be in the range of 0, inclusive, to 360 exclusive; Pitchmay be defined to be in the range of −90 to 90, inclusive.

In an embodiment, the orientation of a spatial region to be overlaid ispre-defined, e.g. in a manner that it is a function of the anglesindicating the position of the spatial region to be overlaid. In anotherembodiment, the orientation of a spatial region to be overlaid isindicated in a manifest and/or parsed from a manifest. For example, aRoll angle indicating a rotation along a third coordinate axis(orthogonal to those coordinate axes around which Yaw and Pitch rotate)may be indicated in a manifest and/or parsed from a manifest, indicatingthe rotation angle of the viewport. In another example, rotation angleis pre-defined to be such that the horizontal axis of the viewport isparallel to an axis in the spherical coordinate system.

In an embodiment, the shape and/or size of the spatial region to beoverlaid are pre-defined. For example, it may be pre-defined that theshape of a spatial region to be overlaid of a cube map is a square andthe size is 90 degrees in horizontal and vertical field of view. In anembodiment, the shape and/or size of the spatial region to be overlaidare indicated in a manifest and/or parsed from a manifest. For example,the manifest may include HorFov and VerFov values, where HorFovindicates the horizontal field of view of the viewport, e.g. in degrees,and VerFov indicates the vertical field of view of the viewport, e.g. indegrees.

In an embodiment, a spatial region to be overlaid is indicated in and/orparsed from a DASH MPD.

If the spatial region to be overlaid is indicated in an Adaptation Setlevel, it applies to all Representations of the Adaptation Set. If theviewport is indicated in a Representation level, it applies to thatRepresentation. If the spatial region to be overlaid is indicated in aSub-Representation level, it applies to that Sub-Representation.

In the above, some embodiments have been described in relation toMPEG-DASH or DASH. It needs to be understood that embodiments similarlyapply to other forms of streaming over HTTP, such as the Apple HTTP LiveStreaming (HLS).

In the above, some embodiments have been described by referring to theterm streaming. It needs to be understood that embodiments similarlyapply to other forms of video transmission, such as progressivedownloading, file delivery, broadcasting, and conversational videocommunications, such as video telephone.

The various embodiments of the invention can be implemented with thehelp of computer program code that resides in a memory and causes therelevant apparatuses to carry out the invention. For example, a devicemay comprise circuitry and electronics for handling, receiving andtransmitting data, computer program code in a memory, and a processorthat, when running the computer program code, causes the device to carryout the features of an embodiment. Yet further, a network device like aserver may comprise circuitry and electronics for handling, receivingand transmitting data, computer program code in a memory, and aprocessor that, when running the computer program code, causes thenetwork device to carry out the features of an embodiment.

If desired, the different functions discussed herein may be performed ina different order and/or concurrently with other. Furthermore, ifdesired, one or more of the above-described functions and embodimentsmay be optional or may be combined.

Although various aspects of the embodiments are set out in theindependent claims, other aspects comprise other combinations offeatures from the described embodiments and/or the dependent claims withthe features of the independent claims, and not solely the combinationsexplicitly set out in the claims.

A recent trend in streaming in order to reduce the streaming bitrate ofvirtual reality video may be known as a viewport dependent delivery andcan be explained as follows: a subset of 360-degree video contentcovering a primary viewport (i.e., the current view orientation) istransmitted at the best quality/resolution, while the remaining of360-degree video is transmitted at a lower quality/resolution. There aregenerally two approaches for viewport-adaptive streaming:

The first approach is viewport-specific encoding and streaming, a.k.a.viewport-dependent encoding and streaming, a.k.a. asymmetric projection.In this approach, 360-degree image content is packed into the same framewith an emphasis (e.g. greater spatial area) on the primary viewport.The packed VR frames are encoded into a single bitstream. For example,the front face of a cube map may be sampled with a higher resolutioncompared to other cube faces and the cube faces may be mapped to thesame packed VR frame as shown in FIG. 3 , where the front cube face issampled with twice the resolution compared to the other cube faces.

The second approach is tile-based encoding and streaming. In thisapproach, 360-degree content is encoded and made available in a mannerthat enables selective streaming of viewports from different encodings.

An approach of tile-based encoding and streaming, which may be referredto as tile rectangle based encoding and streaming or sub-picture basedencoding and streaming, may be used with any video codec, even if tilessimilar to HEVC were not available in the codec or even ifmotion-constrained tile sets or alike were not implemented in anencoder. In tile rectangle based encoding, the source content may besplit into tile rectangle sequences (a.k.a. sub-picture sequences)before encoding. Each tile rectangle sequence covers a subset of thespatial area of the source content, such as full panorama content, whichmay e.g. be of equirectangular projection format. Each tile rectanglesequence may then be encoded independently from each other as asingle-layer bitstream, such as HEVC Main profile bitstream. Severalbitstreams may be encoded from the same tile rectangle sequence, e.g.for different bitrates. Each tile rectangle bitstream may beencapsulated in a file as its own track (or alike) and made availablefor streaming. At the receiver side the tracks to be streamed may beselected based on the viewing orientation. The client may receive trackscovering the entire omnidirectional content. Better quality or higherresolution tracks may be received for the current viewport compared tothe quality or resolution covering the remaining, currently non-visibleviewports. In an example, each track may be decoded with a separatedecoder instance.

In an example of tile rectangle based encoding and streaming, each cubeface may be separately encoded and encapsulated in its own track (andRepresentation). More than one encoded bitstream for each cube face maybe provided, e.g. each with different spatial resolution. Players canchoose tracks (or Representations) to be decoded and played based on thecurrent viewing orientation. High-resolution tracks (or Representations)may be selected for the cube faces used for rendering for the presentviewing orientation, while the remaining cube faces may be obtained fromtheir low-resolution tracks (or Representations).

In an approach of tile-based encoding and streaming, encoding isperformed in a manner that the resulting bitstream comprisesmotion-constrained tile sets. Several bitstreams of the same sourcecontent are encoded using motion-constrained tile sets.

In an approach, one or more motion-constrained tile set sequences areextracted from a bitstream, and each extracted motion-constrained tileset sequence is stored as a tile set track (e.g. an HEVC tile track or afull-picture-compliant tile set track) or a sub-picture track in a file.A tile base track (e.g. an HEVC tile base track or a full picture trackcomprising extractors to extract data from the tile set tracks) may begenerated and stored in a file. The tile base track represents thebitstream by implicitly collecting motion-constrained tile sets from thetile set tracks or by explicitly extracting (e.g. by HEVC extractors)motion-constrained tile sets from the tile set tracks. Tile set tracksand the tile base track of each bitstream may be encapsulated in an ownfile, and the same track identifiers may be used in all files. At thereceiver side the tile set tracks to be streamed may be selected basedon the viewing orientation. The client may receive tile set trackscovering the entire omnidirectional content. Better quality or higherresolution tile set tracks may be received for the current viewportcompared to the quality or resolution covering the remaining, currentlynon-visible viewports.

In an example, equirectangular panorama content is encoded usingmotion-constrained tile sets. More than one encoded bitstream may beprovided, e.g. with different spatial resolution and/or picture quality.Each motion-constrained tile set is made available in its own track (andRepresentation). Players can choose tracks (or Representations) to bedecoded and played based on the current viewing orientation.High-resolution or high-quality tracks (or Representations) may beselected for tile sets covering the present primary viewport, while theremaining area of the 360-degree content may be obtained fromlow-resolution or low-quality tracks (or Representations).

In an approach, each received tile set track is decoded with a separatedecoder or decoder instance.

In another approach, a tile base track is utilized in decoding asfollows. If all the received tile tracks originate from bitstreams ofthe same resolution (or more generally if the tile base tracks of thebitstreams are identical or equivalent, or if the initializationsegments or other initialization data, such as parameter sets, of allthe bitstreams is the same), a tile base track may be received and usedto construct a bitstream. The constructed bitstream may be decoded witha single decoder.

In yet another approach, a first set of tile rectangle tracks and/ortile set tracks may be merged into a first full-picture-compliantbitstream, and a second set of tile rectangle tracks and/or tile settracks may be merged into a second full-picture-compliant bitstream. Thefirst full-picture-compliant bitstream may be decoded with a firstdecoder or decoder instance, and the second full-picture-compliantbitstream may be decoded with a second decoder or decoder instance. Ingeneral, this approach is not limited to two sets of tile rectangletracks and/or tile set tracks, two full-picture-compliant bitstreams, ortwo decoders or decoder instances, but applies to any number of them.With this approach, the client can control the number of paralleldecoders or decoder instances. Moreover, clients that are not capable ofdecoding tile tracks (e.g. HEVC tile tracks) but onlyfull-picture-compliant bitstreams can perform the merging in a mannerthat full-picture-compliant bitstreams are obtained. The merging may besolely performed in the client or full-picture-compliant tile set tracksmay be generated to assist in the merging performed by the client.

A motion-constrained coded sub-picture sequence may be defined as acollective term of such a coded sub-picture sequence in which the codedpictures are motion-constrained pictures, as defined earlier, and anMCTS sequence. Depending on the context of using the termmotion-constrained coded sub-picture sequence, it may be interpreted tomean either one or both of a coded sub-picture sequence in which thecoded pictures are motion-constrained pictures, as defined earlier,and/or an MCTS sequence.

A collector track may be defined as a track that extracts implicitly orexplicitly MCTSs or sub-pictures from other tracks. A collector trackmay be a full-picture-compliant track. A collector track may for exampleextract MCTSs or sub-pictures to form a coded picture sequence whereMCTSs or sub-pictures are arranged to a grid. For example, when acollector track extracts two MCTSs or sub-pictures, they may be arrangedinto a 2×1 grid of MCTSs or sub-pictures. A tile base track may beregarded as a collector track, and an extractor track that extractsMCTSs or sub-pictures from other tracks may be regarded as a collectortrack. A collector track may also be referred to as a collection track.A track that is a source for extracting to a collector track may bereferred to as a collection item track.

The term tile merging (in coded domain) may be defined as a process tomerge coded sub-picture sequences and/or coded MCTS sequences, which mayhave been encapsulated as sub-picture tracks and tile tracks,respectively, into a full-picture-compliant bitstream. A creation of acollector track may be regarded as tile merging that is performed by thefile creator. Resolving a collector track into a full-picture-compliantbitstream may be regarded as tile merging, which is assisted by thecollector track.

It is also possible to combine the first approach (viewport-specificencoding and streaming) and the second approach (tile-based encoding andstreaming) above.

It needs to be understood that tile-based encoding and streaming may berealized by splitting a source picture in sub-picture sequences that arepartly overlapping. Alternatively or additionally, bitstreams withmotion-constrained tile sets may be generated from the same sourcecontent with different tile grids or tile set grids. We could thenimagine the 360 degrees space divided into a discrete set of viewports,each separate by a given distance (e.g., expressed in degrees), so thatthe omnidirectional space can be imagined as a map of overlappingviewports, and the primary viewport is switched discretely as the userchanges his/her orientation while watching content with a head-mounteddisplay. When the overlapping between viewports is reduced to zero, theviewports could be imagined as adjacent non-overlapping tiles within the360 degrees space.

As explained above, in viewport-adaptive streaming the primary viewport(i.e., the current viewing orientation) is transmitted at the bestquality/resolution, while the remaining of 360-degree video istransmitted at a lower quality/resolution. When the viewing orientationchanges, e.g. when the user turns his/her head when viewing the contentwith a head-mounted display, another version of the content needs to bestreamed, matching the new viewing orientation. In general, the newversion can be requested starting from a stream access point (SAP),which are typically aligned with (sub)segments. In single-layer videobitstreams, SAPs are intra-coded and hence costly in terms ofrate-distortion performance. Conventionally, relatively long SAPintervals and consequently relatively long (sub)segment durations in theorder of seconds are hence used. Thus, the delay (here referred to asthe viewport quality update delay) in upgrading the quality after aviewing orientation change (e.g. a head turn) is conventionally in theorder of seconds and is therefore clearly noticeable and may beannoying.

Extractors specified in ISO/IEC 14496-15 for H.264/AVC and HEVC enablecompact formation of tracks that extract NAL unit data by reference. Anextractor is a NAL-unit-like structure. A NAL-unit-like structure may bespecified to comprise a NAL unit header and NAL unit payload like anyNAL units, but start code emulation prevention (that is required for aNAL unit) might not be followed in a NAL-unit-like structure. For HEVC,an extractor contains one or more constructors. A sample constructorextracts, by reference, NAL unit data from a sample of another track. Anin-line constructor includes NAL unit data. When an extractor isprocessed by a file reader that requires it, the extractor is logicallyreplaced by the bytes resulting when resolving the containedconstructors in their appearance order. Nested extraction may bedisallowed, e.g. the bytes referred to by a sample constructor shall notcontain extractors; an extractor shall not reference, directly orindirectly, another extractor. An extractor may contain one or moreconstructors for extracting data from the current track or from anothertrack that is linked to the track in which the extractor resides bymeans of a track reference of type ‘scal’. The bytes of a resolvedextractor may represent one or more entire NAL units. A resolvedextractor starts with a valid length field and a NAL unit header. Thebytes of a sample constructor are copied only from the single identifiedsample in the track referenced through the indicated ‘scal’ trackreference. The alignment is on decoding time, i.e. using thetime-to-sample table only, followed by a counted offset in samplenumber. An extractor track may be defined as a track that contains oneor more extractors.

Extractors are a media-level concept and hence apply to the destinationtrack before any edit list is considered. However, one would normallyexpect that the edit lists in the two tracks would be identical.

The following syntax may be used:

class aligned(8) Extractor ( ) { NALUnitHeader( ); do { unsigned int(8) constructor_type; if( constructor_type == 0 ) SampleConstructor( ); elseif( constructor_type == 2 ) InlineConstructor( ); } while(!EndOfNALUnit( ) ) }

The semantics may be defined as follows:

-   -   NALUnitHeader( ) is the first two bytes of HEVC NAL units. A        particular nal_unit_type value indicates an extractor, e.g.        nal_unit_type equal to 49.    -   constructor_type specifies the constructor being used.    -   EndOfNALUnit( ) is a function that returns 0 (false) when more        data follows in this extractor; otherwise it returns 1 (true).

The sample constructor (SampleConstructor) may have the followingsyntax:

class aligned(8) SampleConstructor ( ) { unsigned int(8)track_ref_index; signed  int(8) sample_offset; unsignedint((lengthSizeMinusOne+1)*8) data_offset; unsignedint((lengthSizeMinusOne+1)*8) data_length; }

track_ref_index identifies the source track from which data isextracted. track_ref_index is the index of the track reference of type‘scal’. The first track reference has the index value 1; the value 0 isreserved.

The sample in that track from which data is extracted is temporallyaligned or nearest preceeding in the media decoding timeline, i.e. usingthe time-to-sample table only, adjusted by an offset specified bysample_offset with the sample containing the extractor. sample_offsetgives the relative index of the sample in the linked track that shall beused as the source of information. Sample 0 (zero) is the sample withthe same, or the closest preceding decoding time compared to thedecoding time of the sample containing the extractor; sample 1 (one) isthe next sample, sample −1 (minus 1) is the previous sample, and so on.

data_offset is the offset of the first byte within the reference sampleto copy. If the extraction starts with the first byte of data in thatsample, the offset takes the value 0.

data_length is the number of bytes to copy.

The syntax of the in-line constructor may be specified as follows:

class aligned(8) InlineConstructor ( ) { unsigned int(8) length;unsigned int(8) inline_data[length]; }

length is the number of bytes that belong to the InlineConstructorfollowing this field, and inline_data is the data bytes to be returnedwhen resolving the in-line constructor.

Coded data of several tile tracks may be merged to one e.g. as follows.

In an approach, the file/segment encapsulation generates pre-constructedtile tracks, which may be full-picture-compliant. Furthermore, thefile/segment encapsulation generates constructed full-picture track(s)that use pre-constructed tile tracks as reference for construction. Theinstructions may be stored in the same file with the segment(s) or mediafile(s), or they may be stored in separate segment hint file(s). Theformat of the instructions may but need not comply with ISOBMFF (or moregenerally the format used for the segment(s) or media file(s)). Forexample, the instructions may form a track (which may be called e.g.MPEG-DASH segment hint track) according to ISOBMFF, and each sample ofthe track may provide instructions to construct a segment or subsegment.

Coded sub-picture sequences may be merged e.g. as follows and asdepicted in FIG. 4 .

The source picture sequence 71 is split 72 into sub-picture sequences 73before encoding. Each sub-picture sequence 73 is then encoded 74independently.

Two or more coded sub-picture sequences 75 are merged 76 into abitstream 77. The coded sub-picture sequences 75 may have differentcharacteristics, such as picture quality, so as to be used forviewport-dependent delivery. The coded sub-pictures 75 of a timeinstance are merged vertically into a coded picture of the bitstream 77.Each coded sub-picture 75 in a coded picture forms a coded slice.Vertical arrangement of the coded sub-pictures 75 into a coded picturemay bring at least the following benefits:

-   -   Slices can be used as a unit to carry a coded sub-picture and no        tile support is needed in the codec, hence the approach is        suitable e.g. for H.264/AVC.    -   No transcoding is needed for the vertical arrangement, as        opposed to horizontal arrangement where transcoding would be        needed as coded sub-pictures would be interleaved in the raster        scan order (i.e., the decoding order) of blocks (e.g.        macroblocks in H.264/AVC or coding tree units in HEVC).    -   Motion vectors that require accessing sample locations        horizontally outside the picture boundaries (in inter        prediction) can be used in the encoding of sub-picture        sequences. Hence, the compression efficiency benefit that comes        from allowing motion vectors over horizontal picture boundaries        is maintained (unlike e.g. when using motion-constrained tile        sets).

The merged bitstream 77 is full-picture compliant. For example, ifsub-picture sequences were coded with H.264/AVC, the merged bitstream isalso compliant with H.264/AVC and can be decoded with a regularH.264/AVC decoder.

In resolution-adaptive MCTS-based viewport-adaptive streaming severalHEVC bitstreams of the same omnidirectional source content are encodedat different resolutions using motion-constrained tile sets. When thebitstreams are encapsulated into file(s), tile tracks are formed fromeach motion-constrained tile set sequence. Clients that are capable ofdecoding HEVC tile streams can receive and decode tile tracksindependently.

In addition to tile tracks, ‘hvc2’/‘hev2’ tracks containing extractors(a.k.a. extractor tracks) can be formed for each expected viewingorientation. An extractor track corresponds to a dependentRepresentation in the DASH MPD, with @dependencyId including theRepresentation identifiers of the tile tracks from which the tile datais extracted. Clients that are not capable of decoding HEVC tile streamsbut only fully compliant HEVC bitstreams can receive and decode theextractor tracks.

FIG. 5 presents an example how extractor tracks can be used fortile-based omnidirectional video streaming. A 4×2 tile grid has beenused in forming of the motion-constrained tile sets 81 a, 81 b. In manyviewing orientations 2×2 tiles out of the 4×2 tile grid are needed tocover a typical field of view of a head-mounted display. In the example,the presented extractor track for high-resolution motion-constrainedtile sets 1, 2, 5 and 6 covers certain viewing orientations, while theextractor track for low-resolution motion-constrained tile sets 3, 4, 7,and 8 includes a region assumed to be non-visible for these viewingorientations. Two HEVC decoders are used in this example, one for thehigh-resolution extractor track and another for the low-resolutionextractor track.

While the description above referred to tile tracks, it should beunderstood that sub-picture tracks can be similarly formed.

Tile merging in coded domain is needed or beneficial for the followingpurposes:

-   -   Enable a number of tiles that is greater than the number of        decoder instances, down to one decoder only    -   Avoid synchronization challenges of multiple decoder instances    -   Reach higher effective spatial and temporal resolutions, e.g. 6        k@60 fps with 4 k@60 fps decoding capacity    -   Enable specifying interoperability points for standards as well        as client APIs that require one decoder only

FIG. 11 is a graphical representation of an example multimediacommunication system within which various embodiments may beimplemented. A data source 1510 provides a source signal in an analog,uncompressed digital, or compressed digital format, or any combinationof these formats. An encoder 1520 may include or be connected with apre-processing, such as data format conversion and/or filtering of thesource signal. The encoder 1520 encodes the source signal into a codedmedia bitstream. It should be noted that a bitstream to be decoded maybe received directly or indirectly from a remote device located withinvirtually any type of network. Additionally, the bitstream may bereceived from local hardware or software. The encoder 1520 may becapable of encoding more than one media type, such as audio and video,or more than one encoder 1520 may be required to code different mediatypes of the source signal. The encoder 1520 may also get syntheticallyproduced input, such as graphics and text, or it may be capable ofproducing coded bitstreams of synthetic media. In the following, onlyprocessing of one coded media bitstream of one media type is consideredto simplify the description. It should be noted, however, that typicallyreal-time broadcast services comprise several streams (typically atleast one audio, video and text sub-titling stream). It should also benoted that the system may include many encoders, but in the figure onlyone encoder 1520 is represented to simplify the description without alack of generality. It should be further understood that, although textand examples contained herein may specifically describe an encodingprocess, one skilled in the art would understand that the same conceptsand principles also apply to the corresponding decoding process and viceversa.

The coded media bitstream may be transferred to a storage 1530. Thestorage 1530 may comprise any type of mass memory to store the codedmedia bitstream. The format of the coded media bitstream in the storage1530 may be an elementary self-contained bitstream format, or one ormore coded media bitstreams may be encapsulated into a container file,or the coded media bitstream may be encapsulated into a Segment formatsuitable for DASH (or a similar streaming system) and stored as asequence of Segments. If one or more media bitstreams are encapsulatedin a container file, a file generator (not shown in the figure) may beused to store the one more media bitstreams in the file and create fileformat metadata, which may also be stored in the file. The encoder 1520or the storage 1530 may comprise the file generator, or the filegenerator is operationally attached to either the encoder 1520 or thestorage 1530. Some systems operate “live”, i.e. omit storage andtransfer coded media bitstream from the encoder 1520 directly to thesender 1540. The coded media bitstream may then be transferred to thesender 1540, also referred to as the server, on a need basis. The formatused in the transmission may be an elementary self-contained bitstreamformat, a packet stream format, a Segment format suitable for DASH (or asimilar streaming system), or one or more coded media bitstreams may beencapsulated into a container file. The encoder 1520, the storage 1530,and the server 1540 may reside in the same physical device or they maybe included in separate devices. The encoder 1520 and server 1540 mayoperate with live real-time content, in which case the coded mediabitstream is typically not stored permanently, but rather buffered forsmall periods of time in the content encoder 1520 and/or in the server1540 to smooth out variations in processing delay, transfer delay, andcoded media bitrate.

The server 1540 sends the coded media bitstream using a communicationprotocol stack. The stack may include but is not limited to one or moreof Hypertext Transfer Protocol (HTTP), Transmission Control Protocol(TCP), and Internet Protocol (IP). When the communication protocol stackis packet-oriented, the server 1540 encapsulates the coded mediabitstream into packets. It should be again noted that a system maycontain more than one server 1540, but for the sake of simplicity, thefollowing description only considers one server 1540.

If the media content is encapsulated in a container file for the storage1530 or for inputting the data to the sender 1540, the sender 1540 maycomprise or be operationally attached to a “sending file parser” (notshown in the figure). In particular, if the container file is nottransmitted as such but at least one of the contained coded mediabitstream is encapsulated for transport over a communication protocol, asending file parser locates appropriate parts of the coded mediabitstream to be conveyed over the communication protocol. The sendingfile parser may also help in creating the correct format for thecommunication protocol, such as packet headers and payloads. Themultimedia container file may contain encapsulation instructions, suchas hint tracks in the ISOBMFF, for encapsulation of the at least one ofthe contained media bitstream on the communication protocol.

The server 1540 may or may not be connected to a gateway 1550 through acommunication network, which may e.g. be a combination of a CDN, theInternet and/or one or more access networks. The gateway may also oralternatively be referred to as a middle-box. For DASH, the gateway maybe an edge server (of a CDN) or a web proxy. It is noted that the systemmay generally comprise any number gateways or alike, but for the sake ofsimplicity, the following description only considers one gateway 1550.The gateway 1550 may perform different types of functions, such astranslation of a packet stream according to one communication protocolstack to another communication protocol stack, merging and forking ofdata streams, and manipulation of data stream according to the downlinkand/or receiver capabilities, such as controlling the bit rate of theforwarded stream according to prevailing downlink network conditions.

The system includes one or more receivers 1560, typically capable ofreceiving, de-modulating, and de-capsulating the transmitted signal intoa coded media bitstream. The coded media bitstream may be transferred toa recording storage 1570. The recording storage 1570 may comprise anytype of mass memory to store the coded media bitstream. The recordingstorage 1570 may alternatively or additively comprise computationmemory, such as random access memory. The format of the coded mediabitstream in the recording storage 1570 may be an elementaryself-contained bitstream format, or one or more coded media bitstreamsmay be encapsulated into a container file. If there are multiple codedmedia bitstreams, such as an audio stream and a video stream, associatedwith each other, a container file is typically used and the receiver1560 comprises or is attached to a container file generator producing acontainer file from input streams. Some systems operate “live,” i.e.omit the recording storage 1570 and transfer coded media bitstream fromthe receiver 1560 directly to the decoder 1580. In some systems, onlythe most recent part of the recorded stream, e.g., the most recent10-minute excerption of the recorded stream, is maintained in therecording storage 1570, while any earlier recorded data is discardedfrom the recording storage 1570.

The coded media bitstream may be transferred from the recording storage1570 to the decoder 1580. If there are many coded media bitstreams, suchas an audio stream and a video stream, associated with each other andencapsulated into a container file or a single media bitstream isencapsulated in a container file e.g. for easier access, a file parser(not shown in the figure) is used to decapsulate each coded mediabitstream from the container file. The recording storage 1570 or adecoder 1580 may comprise the file parser, or the file parser isattached to either recording storage 1570 or the decoder 1580. It shouldalso be noted that the system may include many decoders, but here onlyone decoder 1570 is discussed to simplify the description without a lackof generality

The coded media bitstream may be processed further by a decoder 1570,whose output is one or more uncompressed media streams. Finally, arenderer 1590 may reproduce the uncompressed media streams with aloudspeaker or a display, for example. The receiver 1560, recordingstorage 1570, decoder 1570, and renderer 1590 may reside in the samephysical device or they may be included in separate devices.

A sender 1540 and/or a gateway 1550 may be configured to performswitching between different representations e.g. for view switching,bitrate adaptation and/or fast start-up, and/or a sender 1540 and/or agateway 1550 may be configured to select the transmittedrepresentation(s). Switching between different representations may takeplace for multiple reasons, such as to respond to requests of thereceiver 1560 or prevailing conditions, such as throughput, of thenetwork over which the bitstream is conveyed. A request from thereceiver can be, e.g., a request for a Segment or a Subsegment from adifferent representation than earlier, a request for a change oftransmitted scalability layers and/or sub-layers, or a change of arendering device having different capabilities compared to the previousone. A request for a Segment may be an HTTP GET request. A request for aSubsegment may be an HTTP GET request with a byte range. Additionally oralternatively, bitrate adjustment or bitrate adaptation may be used forexample for providing so-called fast start-up in streaming services,where the bitrate of the transmitted stream is lower than the channelbitrate after starting or random-accessing the streaming in order tostart playback immediately and to achieve a buffer occupancy level thattolerates occasional packet delays and/or retransmissions. Bitrateadaptation may include multiple representation or layer up-switching andrepresentation or layer down-switching operations taking place invarious orders.

A decoder 1580 may be configured to perform switching between differentrepresentations e.g. for view switching, bitrate adaptation and/or faststart-up, and/or a decoder 1580 may be configured to select thetransmitted representation(s). Switching between differentrepresentations may take place for multiple reasons, such as to achievefaster decoding operation or to adapt the transmitted bitstream, e.g. interms of bitrate, to prevailing conditions, such as throughput, of thenetwork over which the bitstream is conveyed. Faster decoding operationmight be needed for example if the device including the decoder 580 ismulti-tasking and uses computing resources for other purposes thandecoding the scalable video bitstream. In another example, fasterdecoding operation might be needed when content is played back at afaster pace than the normal playback speed, e.g. twice or three timesfaster than conventional real-time playback rate. The speed of decoderoperation may be changed during the decoding or playback for example asresponse to changing from a fast-forward play from normal playback rateor vice versa, and consequently multiple layer up-switching and layerdown-switching operations may take place in various orders.

In the above, many embodiments have been described with reference to theequirectangular projection format. It needs to be understood thatembodiments similarly apply to equirectangular pictures where thevertical coverage is less than 180 degrees. For example, the coveredelevation range may be from −75° to 75°, or from −60° to 90° (i.e.,covering one both not both poles). It also needs to be understood thatembodiments similarly cover horizontally segmented equirectangularprojection format, where a horizontal segment covers an azimuth range of360 degrees and may have a resolution potentially differing from theresolution of other horizontal segments. Furthermore, it needs to beunderstood that embodiments similarly apply to omnidirectional pictureformats, where a first sphere region of the content is represented bythe equirectangular projection of limited elevation range and a secondsphere region of the content is represented by another projection, suchas cube map projection. For example, the elevation range −45° to 45° maybe represented by a “middle” region of equirectangular projection, andthe other sphere regions may be represented by a rectilinear projection,similar to cube faces of a cube map but where the corners overlappingwith the middle region on the spherical domain are cut out. In suchcases, embodiments can be applied to the middle region represented bythe equirectangular projection.

In the above, some embodiments have been described with reference toterminology of particular codecs, most notably HEVC. It needs to beunderstood that embodiments can be similarly realized with respectiveterms of other codecs. For example, rather than tiles or tile sets,embodiments could be realized with rectangular slice groups ofH.264/AVC.

The phrase along the bitstream (e.g. indicating along the bitstream) maybe used in claims and described embodiments to refer to out-of-bandtransmission, signaling, or storage in a manner that the out-of-banddata is associated with the bitstream. The phrase decoding along thebitstream or alike may refer to decoding the referred out-of-band data(which may be obtained from out-of-band transmission, signaling, orstorage) that is associated with the bitstream.

The phrase along the track (e.g. including, along a track, a descriptionof a motion-constrained coded sub-picture sequence) may be used inclaims and described embodiments to refer to out-of-band transmission,signaling, or storage in a manner that the out-of-band data isassociated with the track. In other words, the phrase “a descriptionalong the track” may be understood to mean that the description is notstored in the file or segments that carry the track, but within anotherresource, such as a media presentation description. For example, thedescription of the motion-constrained coded sub-picture sequence may beincluded in a media presentation description that includes informationof a Representation conveying the track. The phrase decoding along thetrack or alike may refer to decoding the referred out-of-band data(which may be obtained from out-of-band transmission, signaling, orstorage) that is associated with the track.

In the above, some embodiments have been described with reference tosegments, e.g. as defined in MPEG-DASH. It needs to be understood thatembodiments may be similarly realized with subsegments, e.g. as definedin MPEG-DASH.

In the above, some embodiments have been described in relation to DASHor MPEG-DASH. It needs to be understood that embodiments could besimilarly realized with any other similar streaming system, and/or anysimilar protocols as those used in DASH, and/or any similar segmentand/or manifest formats as those used in DASH, and/or any similar clientoperation as that of a DASH client. For example, some embodiments couldbe realized with the M3U manifest format.

In the above, some embodiments have been described in relation toISOBMFF, e.g. when it comes to segment format. It needs to be understoodthat embodiments could be similarly realized with any other file format,such as Matroska, with similar capability and/or structures as those inISOBMFF.

In the above, some embodiments have been described with reference toencoding or including indications or metadata in the bitstream and/ordecoding indications or metadata from the bitstream. It needs to beunderstood that indications or metadata may additionally oralternatively be encoded or included along the bitstream and/or decodedalong the bitstream. For example, indications or metadata may beincluded in or decoded from a container file that encapsulates thebitstream.

In the above, some embodiments have been described with reference toincluding metadata or indications in or along a container file and/orparsing or decoding metadata and/or indications from or along acontainer file. It needs to be understood that indications or metadatamay additionally or alternatively be encoded or included in the videobitstream, for example as SEI message(s) or VUI, and/or decoded in thevideo bitstream, for example from SEI message(s) or VUI.

The following describes in further detail suitable apparatus andpossible mechanisms for implementing the embodiments of the invention.In this regard reference is first made to FIG. 12 which shows aschematic block diagram of an exemplary apparatus or electronic device50 depicted in FIG. 13 , which may incorporate a transmitter accordingto an embodiment of the invention.

The electronic device 50 may for example be a mobile terminal or userequipment of a wireless communication system. However, it would beappreciated that embodiments of the invention may be implemented withinany electronic device or apparatus which may require transmission ofradio frequency signals.

The apparatus 50 may comprise a housing 30 for incorporating andprotecting the device. The apparatus 50 further may comprise a display32 in the form of a liquid crystal display. In other embodiments of theinvention the display may be any suitable display technology suitable todisplay an image or video. The apparatus 50 may further comprise akeypad 34. In other embodiments of the invention any suitable data oruser interface mechanism may be employed. For example the user interfacemay be implemented as a virtual keyboard or data entry system as part ofa touch-sensitive display. The apparatus may comprise a microphone 36 orany suitable audio input which may be a digital or analogue signalinput. The apparatus 50 may further comprise an audio output devicewhich in embodiments of the invention may be any one of: an earpiece 38,speaker, or an analogue audio or digital audio output connection. Theapparatus 50 may also comprise a battery 40 (or in other embodiments ofthe invention the device may be powered by any suitable mobile energydevice such as solar cell, fuel cell or clockwork generator). The termbattery discussed in connection with the embodiments may also be one ofthese mobile energy devices. Further, the apparatus 50 may comprise acombination of different kinds of energy devices, for example arechargeable battery and a solar cell. The apparatus may furthercomprise an infrared port 41 for short range line of sight communicationto other devices. In other embodiments the apparatus 50 may furthercomprise any suitable short range communication solution such as forexample a Bluetooth wireless connection or a USB/FireWire wiredconnection.

The apparatus 50 may comprise a controller 56 or processor forcontrolling the apparatus 50. The controller 56 may be connected tomemory 58 which in embodiments of the invention may store both dataand/or may also store instructions for implementation on the controller56. The controller 56 may further be connected to codec circuitry 54suitable for carrying out coding and decoding of audio and/or video dataor assisting in coding and decoding carried out by the controller 56.

The apparatus 50 may further comprise a card reader 48 and a smart card46, for example a universal integrated circuit card (UICC) reader and auniversal integrated circuit card for providing user information andbeing suitable for providing authentication information forauthentication and authorization of the user at a network.

The apparatus 50 may comprise radio interface circuitry 52 connected tothe controller and suitable for generating wireless communicationsignals for example for communication with a cellular communicationsnetwork, a wireless communications system or a wireless local areanetwork. The apparatus 50 may further comprise an antenna 60 connectedto the radio interface circuitry 52 for transmitting radio frequencysignals generated at the radio interface circuitry 52 to otherapparatus(es) and for receiving radio frequency signals from otherapparatus(es).

In some embodiments of the invention, the apparatus 50 comprises acamera 42 capable of recording or detecting imaging.

With respect to FIG. 14 , an example of a system within whichembodiments of the present invention can be utilized is shown. Thesystem 10 comprises multiple communication devices which can communicatethrough one or more networks. The system 10 may comprise any combinationof wired and/or wireless networks including, but not limited to awireless cellular telephone network (such as a global systems for mobilecommunications (GSM), universal mobile telecommunications system (UMTS),long term evolution (LTE) based network, code division multiple access(CDMA) network etc.), a wireless local area network (WLAN) such asdefined by any of the IEEE 802.x standards, a Bluetooth personal areanetwork, an Ethernet local area network, a token ring local areanetwork, a wide area network, and the Internet.

For example, the system shown in FIG. 14 shows a mobile telephonenetwork 11 and a representation of the internet 28. Connectivity to theinternet 28 may include, but is not limited to, long range wirelessconnections, short range wireless connections, and various wiredconnections including, but not limited to, telephone lines, cable lines,power lines, and similar communication pathways.

The example communication devices shown in the system 10 may include,but are not limited to, an electronic device or apparatus 50, acombination of a personal digital assistant (PDA) and a mobile telephone14, a PDA 16, an integrated messaging device (IMD) 18, a desktopcomputer 20, a notebook computer 22, a tablet computer. The apparatus 50may be stationary or mobile when carried by an individual who is moving.The apparatus 50 may also be located in a mode of transport including,but not limited to, a car, a truck, a taxi, a bus, a train, a boat, anairplane, a bicycle, a motorcycle or any similar suitable mode oftransport.

Some or further apparatus may send and receive calls and messages andcommunicate with service providers through a wireless connection 25 to abase station 24. The base station 24 may be connected to a networkserver 26 that allows communication between the mobile telephone network11 and the internet 28. The system may include additional communicationdevices and communication devices of various types.

The communication devices may communicate using various transmissiontechnologies including, but not limited to, code division multipleaccess (CDMA), global systems for mobile communications (GSM), universalmobile telecommunications system (UMTS), time divisional multiple access(TDMA), frequency division multiple access (FDMA), transmission controlprotocol-internet protocol (TCP-IP), short messaging service (SMS),multimedia messaging service (MMS), email, instant messaging service(IMS), Bluetooth, IEEE 802.11, Long Term Evolution wirelesscommunication technique (LTE) and any similar wireless communicationtechnology. A communications device involved in implementing variousembodiments of the present invention may communicate using various mediaincluding, but not limited to, radio, infrared, laser, cableconnections, and any suitable connection.

Although the above examples describe embodiments of the inventionoperating within a wireless communication device, it would beappreciated that the invention as described above may be implemented asa part of any apparatus comprising a circuitry in which radio frequencysignals are transmitted and received. Thus, for example, embodiments ofthe invention may be implemented in a mobile phone, in a base station,in a computer such as a desktop computer or a tablet computer comprisingradio frequency communication means (e.g. wireless local area network,cellular radio, etc.).

In general, the various embodiments of the invention may be implementedin hardware or special purpose circuits or any combination thereof.While various aspects of the invention may be illustrated and describedas block diagrams or using some other pictorial representation, it iswell understood that these blocks, apparatus, systems, techniques ormethods described herein may be implemented in, as non-limitingexamples, hardware, software, firmware, special purpose circuits orlogic, general purpose hardware or controller or other computingdevices, or some combination thereof.

Embodiments of the inventions may be practiced in various componentssuch as integrated circuit modules. The design of integrated circuits isby and large a highly automated process. Complex and powerful softwaretools are available for converting a logic level design into asemiconductor circuit design ready to be etched and formed on asemiconductor substrate.

Programs, such as those provided by Synopsys, Inc. of Mountain View,Calif. and Cadence Design, of San Jose, Calif. automatically routeconductors and locate components on a semiconductor chip using wellestablished rules of design as well as libraries of pre-stored designmodules. Once the design for a semiconductor circuit has been completed,the resultant design, in a standardized electronic format (e.g., Opus,GDSII, or the like) may be transmitted to a semiconductor fabricationfacility or “fab” for fabrication.

The foregoing description has provided by way of exemplary andnon-limiting examples a full and informative description of theexemplary embodiment of this invention. However, various modificationsand adaptations may become apparent to those skilled in the relevantarts in view of the foregoing description, when read in conjunction withthe accompanying drawings and the appended claims. However, all such andsimilar modifications of the teachings of this invention will still fallwithin the scope of this invention.

The invention claimed is:
 1. A method comprising: obtaining informationof a region for overlaying at least a part of an omnidirectional video,wherein the region for overlaying comprises, at least, a recommendedviewport; obtaining information of a current viewport in theomnidirectional video; obtaining information of an overlaying method fordetermining whether to overlay a part of the current viewport by theregion for overlaying, wherein the information of the overlaying methodcomprises at least one condition; and encoding the information of theregion for overlaying, the information of the current viewport and theinformation of the overlaying method, wherein the encoding is configuredto enable overlaying of the part of the current viewport by the regionfor overlaying based on the overlaying method in response to adetermination to perform overlaying.
 2. The method according to claim 1,wherein the part of the current viewport to be overlaid by the regionfor overlaying is indicated by a reference point at the current viewportand as percentages of width and height of the current viewport.
 3. Themethod according to claim 2, wherein the reference point comprises atop-left corner of the current viewport.
 4. An apparatus comprising atleast one processor and at least one non-transitory memory, said atleast one memory stored with code thereon, which when executed by saidat least one processor, causes the apparatus to perform at least: obtaininformation of a region for overlaying at least a part of anomnidirectional video, wherein the region for overlaying comprises, atleast, a recommended viewport; obtain information of a current viewportin the omnidirectional video; obtain information of an overlaying methodfor determining whether to overlay a part of the current viewport by theregion for overlaying, wherein the information of the overlaying methodcomprises at least one condition; and encode the information of theregion for overlaying, the information of the current viewport and theinformation of the overlaying method, wherein the encoding is configuredto enable overlaying of the part of the current viewport by the regionfor overlaying based on the overlaying method in response to adetermination to overlay.
 5. The apparatus according to claim 4, whereinthe part of the current viewport to be overlaid by the region foroverlaying is indicated by a reference point at the current viewport andas percentages of width and height of the current viewport.
 6. Theapparatus according to claim 5, wherein the reference point comprises atop-left corner of the current viewport.
 7. The apparatus according toclaim 4, wherein the at least one memory stored with the code thereon,which when executed by the at least one processor, causes the apparatusto obtain information of a relative disparity of the region foroverlaying, wherein the relative disparity is configured to indicate adepth applicable for the region for overlaying.
 8. A method comprising:receiving information of a region for overlaying at least a part of anomnidirectional video, wherein the region for overlaying comprises, atleast, a recommended viewport; receiving information of a currentviewport in the omnidirectional video; receiving information of anoverlaying method for determining whether to overlay a part of thecurrent viewport by the region for overlaying, wherein the informationof the overlaying method comprises at least one condition; decoding theinformation of the overlaying method; decoding image information of thecurrent viewport; decoding image information of the region foroverlaying; examining the decoded information of the overlaying methodto determine whether to overlay the part of the current viewport by theregion for overlaying; and overlaying the part of the current viewportby the region for overlaying in response to a determination to overlaythe part of the current viewport by the region for overlaying.
 9. Themethod according to claim 8, wherein the part of the current viewport tobe overlaid by the region for overlaying is indicated by a referencepoint at the current viewport and as percentages of width and height ofthe current viewport.
 10. The method according to claim 9, wherein thereference point comprises a top-left corner of the current viewport. 11.The method according to claim 8, further comprising obtaininginformation of a relative disparity of the region for overlaying,wherein the relative disparity is configured to indicate a depthapplicable for the region for overlaying.
 12. The method according toclaim 8, further comprising: decoding information of one or more levelsof transparency for the region for overlaying; and using the decodedinformation of the one or more levels of transparency in overlaying theregion for overlaying.
 13. An apparatus comprising at least oneprocessor and at least one non-transitory memory, said at least onememory stored with code thereon, which when executed by said at leastone processor, causes the apparatus to perform at least: receiveinformation of a region for overlaying at least a part of anomnidirectional video, wherein the region for overlaying comprises, atleast, a recommended viewport; receive information of a current viewportin the omnidirectional video; receive information of an overlayingmethod for determining whether to overlay a part of the current viewportby the region for overlaying, wherein the information of the overlayingmethod comprises at least one condition; decode the information of theoverlaying method; decode image information of the current viewport;decode image information of the region for overlaying; examine thedecoded information of the overlaying method to determine whether tooverlay the part of the current viewport by the region for overlaying;and overlay the part of the current viewport by the region foroverlaying in response to a determination to overlay the part of thecurrent viewport by the region for overlaying.
 14. The apparatusaccording to claim 13, wherein the part of the current viewport to beoverlaid by the region for overlaying is indicated by a reference pointat the current viewport and as percentages of width and height of thecurrent viewport.
 15. The apparatus according to claim 14, wherein thereference point comprises a top-left corner of the current viewport. 16.The apparatus according to claim 13, wherein the at least one memorystored with the code thereon, which when executed by the at least oneprocessor, causes the apparatus to obtain information of a relativedisparity of the region for overlaying.
 17. The apparatus according toclaim 13, said at least one memory stored with the code thereon, whichwhen executed by said at least one processor, causes the apparatus to:decode information of one or more levels of transparency for the regionfor overlaying; and use the decoded information of the one or morelevels of transparency in overlaying the region for overlaying.